| Message ID | 20230925144842.586829-3-michal.wilczynski@intel.com |
|---|---|
| State | New |
| Headers | show |
| Series | Replace acpi_driver with platform_driver | expand |
On Monday, September 25, 2023 4:48:35 PM CEST Michal Wilczynski wrote: > Some devices implement ACPI driver as a way to manage devices > enumerated by the ACPI. This might be confusing as a preferred way to > implement a driver for devices not connected to any bus is a platform > driver, as stated in the documentation. Clarify relationships between > ACPI device, platform device and ACPI entries. > > Suggested-by: Elena Reshetova <elena.reshetova@intel.com> > Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> > --- > Documentation/firmware-guide/acpi/enumeration.rst | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst > index 56d9913a3370..f56cc79a9e83 100644 > --- a/Documentation/firmware-guide/acpi/enumeration.rst > +++ b/Documentation/firmware-guide/acpi/enumeration.rst > @@ -64,6 +64,19 @@ If the driver needs to perform more complex initialization like getting and > configuring GPIOs it can get its ACPI handle and extract this information > from ACPI tables. > > +ACPI bus > +==================== > + > +Historically some devices not connected to any bus were represented as ACPI > +devices, and had to implement ACPI driver. This is not a preferred way for new > +drivers. As explained above devices not connected to any bus should implement > +platform driver. ACPI device would be created during enumeration nonetheless, > +and would be accessible through ACPI_COMPANION() macro, and the ACPI handle would > +be accessible through ACPI_HANDLE() macro. ACPI device is meant to describe > +information related to ACPI entry e.g. handle of the ACPI entry. Think - > +ACPI device interfaces with the FW, and the platform device with the rest of > +the system. > + > DMA support > =========== I rewrote the above entirely, so here's a new patch to replace this one: --- From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Subject: [PATCH v2 2/9] ACPI: docs: enumeration: Clarify ACPI bus concepts In some cases, ACPI drivers are implemented as a way to manage devices enumerated with the help of the platform firmware through ACPI. This might be confusing, since the preferred way to implement a driver for a device that cannot be enumerated natively, is a platform driver, as stated in the documentation. Clarify relationships between ACPI device objects, platform devices and ACPI Namespace entries. Suggested-by: Elena Reshetova <elena.reshetova@intel.com> Co-developed-by: Michal Wilczynski <michal.wilczynski@intel.com> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> --- Documentation/firmware-guide/acpi/enumeration.rst | 43 ++++++++++++++++++++++ 1 file changed, 43 insertions(+) Index: linux-pm/Documentation/firmware-guide/acpi/enumeration.rst =================================================================== --- linux-pm.orig/Documentation/firmware-guide/acpi/enumeration.rst +++ linux-pm/Documentation/firmware-guide/acpi/enumeration.rst @@ -64,6 +64,49 @@ If the driver needs to perform more comp configuring GPIOs it can get its ACPI handle and extract this information from ACPI tables. +ACPI device objects +=================== + +Generally speaking, there are two categories of devices in a system in which +ACPI is used as an interface between the platform firmware and the OS: Devices +that can be discovered and enumerated natively, through a protocol defined for +the specific bus that they are on (for example, configuration space in PCI), +without the platform firmware assistance, and devices that need to be described +by the platform firmware so that they can be discovered. Still, for any device +known to the platform firmware, regardless of which category it falls into, +there can be a corresponding ACPI device object in the ACPI Namespace in which +case the Linux kernel will create a struct acpi_device object based on it for +that device. + +Those struct acpi_device objects are never used for binding drivers to natively +discoverable devices, because they are represented by other types of device +objects (for example, struct pci_dev for PCI devices) that are bound to by +device drivers (the corresponding struct acpi_device object is then used as +an additional source of information on the configuration of the given device). +Moreover, the core ACPI device enumeration code creates struct platform_device +objects for the majority of devices that are discovered and enumerated with the +help of the platform firmware and those platform device objects can be bound to +by platform drivers in direct analogy with the natively enumerable devices +case. Therefore it is logically inconsistent and so generally invalid to bind +drivers to struct acpi_device objects, including drivers for devices that are +discovered with the help of the platform firmware. + +Historically, ACPI drivers that bound directly to struct acpi_device objects +were implemented for some devices enumerated with the help of the platform +firmware, but this is not recommended for any new drivers. As explained above, +platform device objects are created for those devices as a rule (with a few +exceptions that are not relevant here) and so platform drivers should be used +for handling them, even though the corresponding ACPI device objects are the +only source of device configuration information in that case. + +For every device having a corresponding struct acpi_device object, the pointer +to it is returned by the ACPI_COMPANION() macro, so it is always possible to +get to the device configuration information stored in the ACPI device object +this way. Accordingly, struct acpi_device can be regarded as a part of the +interface between the kernel and the ACPI Namespace, whereas device objects of +other types (for example, struct pci_dev or struct platform_device) are used +for interacting with the rest of the system. + DMA support ===========
On 10/5/2023 7:57 PM, Rafael J. Wysocki wrote: > On Monday, September 25, 2023 4:48:35 PM CEST Michal Wilczynski wrote: >> Some devices implement ACPI driver as a way to manage devices >> enumerated by the ACPI. This might be confusing as a preferred way to >> implement a driver for devices not connected to any bus is a platform >> driver, as stated in the documentation. Clarify relationships between >> ACPI device, platform device and ACPI entries. >> >> Suggested-by: Elena Reshetova <elena.reshetova@intel.com> >> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> >> --- >> Documentation/firmware-guide/acpi/enumeration.rst | 13 +++++++++++++ >> 1 file changed, 13 insertions(+) >> >> diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst >> index 56d9913a3370..f56cc79a9e83 100644 >> --- a/Documentation/firmware-guide/acpi/enumeration.rst >> +++ b/Documentation/firmware-guide/acpi/enumeration.rst >> @@ -64,6 +64,19 @@ If the driver needs to perform more complex initialization like getting and >> configuring GPIOs it can get its ACPI handle and extract this information >> from ACPI tables. >> >> +ACPI bus >> +==================== >> + >> +Historically some devices not connected to any bus were represented as ACPI >> +devices, and had to implement ACPI driver. This is not a preferred way for new >> +drivers. As explained above devices not connected to any bus should implement >> +platform driver. ACPI device would be created during enumeration nonetheless, >> +and would be accessible through ACPI_COMPANION() macro, and the ACPI handle would >> +be accessible through ACPI_HANDLE() macro. ACPI device is meant to describe >> +information related to ACPI entry e.g. handle of the ACPI entry. Think - >> +ACPI device interfaces with the FW, and the platform device with the rest of >> +the system. >> + >> DMA support >> =========== > I rewrote the above entirely, so here's a new patch to replace this one: > > --- > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Subject: [PATCH v2 2/9] ACPI: docs: enumeration: Clarify ACPI bus concepts > > In some cases, ACPI drivers are implemented as a way to manage devices > enumerated with the help of the platform firmware through ACPI. > > This might be confusing, since the preferred way to implement a driver > for a device that cannot be enumerated natively, is a platform > driver, as stated in the documentation. > > Clarify relationships between ACPI device objects, platform devices and > ACPI Namespace entries. > > Suggested-by: Elena Reshetova <elena.reshetova@intel.com> > Co-developed-by: Michal Wilczynski <michal.wilczynski@intel.com> > Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > --- > Documentation/firmware-guide/acpi/enumeration.rst | 43 ++++++++++++++++++++++ > 1 file changed, 43 insertions(+) > > Index: linux-pm/Documentation/firmware-guide/acpi/enumeration.rst > =================================================================== > --- linux-pm.orig/Documentation/firmware-guide/acpi/enumeration.rst > +++ linux-pm/Documentation/firmware-guide/acpi/enumeration.rst > @@ -64,6 +64,49 @@ If the driver needs to perform more comp > configuring GPIOs it can get its ACPI handle and extract this information > from ACPI tables. > > +ACPI device objects > +=================== > + > +Generally speaking, there are two categories of devices in a system in which > +ACPI is used as an interface between the platform firmware and the OS: Devices > +that can be discovered and enumerated natively, through a protocol defined for > +the specific bus that they are on (for example, configuration space in PCI), > +without the platform firmware assistance, and devices that need to be described > +by the platform firmware so that they can be discovered. Still, for any device > +known to the platform firmware, regardless of which category it falls into, > +there can be a corresponding ACPI device object in the ACPI Namespace in which > +case the Linux kernel will create a struct acpi_device object based on it for > +that device. > + > +Those struct acpi_device objects are never used for binding drivers to natively > +discoverable devices, because they are represented by other types of device > +objects (for example, struct pci_dev for PCI devices) that are bound to by > +device drivers (the corresponding struct acpi_device object is then used as > +an additional source of information on the configuration of the given device). > +Moreover, the core ACPI device enumeration code creates struct platform_device > +objects for the majority of devices that are discovered and enumerated with the > +help of the platform firmware and those platform device objects can be bound to > +by platform drivers in direct analogy with the natively enumerable devices > +case. Therefore it is logically inconsistent and so generally invalid to bind > +drivers to struct acpi_device objects, including drivers for devices that are > +discovered with the help of the platform firmware. > + > +Historically, ACPI drivers that bound directly to struct acpi_device objects > +were implemented for some devices enumerated with the help of the platform > +firmware, but this is not recommended for any new drivers. As explained above, > +platform device objects are created for those devices as a rule (with a few > +exceptions that are not relevant here) and so platform drivers should be used > +for handling them, even though the corresponding ACPI device objects are the > +only source of device configuration information in that case. > + > +For every device having a corresponding struct acpi_device object, the pointer > +to it is returned by the ACPI_COMPANION() macro, so it is always possible to > +get to the device configuration information stored in the ACPI device object > +this way. Accordingly, struct acpi_device can be regarded as a part of the > +interface between the kernel and the ACPI Namespace, whereas device objects of > +other types (for example, struct pci_dev or struct platform_device) are used > +for interacting with the rest of the system. > + > DMA support > =========== Thanks a lot ! Looks very good, will include this in next revision. Michał > > > >
On 10/5/2023 8:28 PM, Wilczynski, Michal wrote: > > On 10/5/2023 7:57 PM, Rafael J. Wysocki wrote: >> On Monday, September 25, 2023 4:48:35 PM CEST Michal Wilczynski wrote: >>> Some devices implement ACPI driver as a way to manage devices >>> enumerated by the ACPI. This might be confusing as a preferred way to >>> implement a driver for devices not connected to any bus is a platform >>> driver, as stated in the documentation. Clarify relationships between >>> ACPI device, platform device and ACPI entries. >>> >>> Suggested-by: Elena Reshetova <elena.reshetova@intel.com> >>> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> >>> --- >>> Documentation/firmware-guide/acpi/enumeration.rst | 13 +++++++++++++ >>> 1 file changed, 13 insertions(+) >>> >>> diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst >>> index 56d9913a3370..f56cc79a9e83 100644 >>> --- a/Documentation/firmware-guide/acpi/enumeration.rst >>> +++ b/Documentation/firmware-guide/acpi/enumeration.rst >>> @@ -64,6 +64,19 @@ If the driver needs to perform more complex initialization like getting and >>> configuring GPIOs it can get its ACPI handle and extract this information >>> from ACPI tables. >>> >>> +ACPI bus >>> +==================== >>> + >>> +Historically some devices not connected to any bus were represented as ACPI >>> +devices, and had to implement ACPI driver. This is not a preferred way for new >>> +drivers. As explained above devices not connected to any bus should implement >>> +platform driver. ACPI device would be created during enumeration nonetheless, >>> +and would be accessible through ACPI_COMPANION() macro, and the ACPI handle would >>> +be accessible through ACPI_HANDLE() macro. ACPI device is meant to describe >>> +information related to ACPI entry e.g. handle of the ACPI entry. Think - >>> +ACPI device interfaces with the FW, and the platform device with the rest of >>> +the system. >>> + >>> DMA support >>> =========== >> I rewrote the above entirely, so here's a new patch to replace this one: >> >> --- >> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >> Subject: [PATCH v2 2/9] ACPI: docs: enumeration: Clarify ACPI bus concepts >> >> In some cases, ACPI drivers are implemented as a way to manage devices >> enumerated with the help of the platform firmware through ACPI. >> >> This might be confusing, since the preferred way to implement a driver >> for a device that cannot be enumerated natively, is a platform >> driver, as stated in the documentation. >> >> Clarify relationships between ACPI device objects, platform devices and >> ACPI Namespace entries. >> >> Suggested-by: Elena Reshetova <elena.reshetova@intel.com> >> Co-developed-by: Michal Wilczynski <michal.wilczynski@intel.com> >> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> >> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >> --- >> Documentation/firmware-guide/acpi/enumeration.rst | 43 ++++++++++++++++++++++ >> 1 file changed, 43 insertions(+) >> >> Index: linux-pm/Documentation/firmware-guide/acpi/enumeration.rst >> =================================================================== >> --- linux-pm.orig/Documentation/firmware-guide/acpi/enumeration.rst >> +++ linux-pm/Documentation/firmware-guide/acpi/enumeration.rst >> @@ -64,6 +64,49 @@ If the driver needs to perform more comp >> configuring GPIOs it can get its ACPI handle and extract this information >> from ACPI tables. >> >> +ACPI device objects >> +=================== >> + >> +Generally speaking, there are two categories of devices in a system in which >> +ACPI is used as an interface between the platform firmware and the OS: Devices >> +that can be discovered and enumerated natively, through a protocol defined for >> +the specific bus that they are on (for example, configuration space in PCI), >> +without the platform firmware assistance, and devices that need to be described >> +by the platform firmware so that they can be discovered. Still, for any device >> +known to the platform firmware, regardless of which category it falls into, >> +there can be a corresponding ACPI device object in the ACPI Namespace in which >> +case the Linux kernel will create a struct acpi_device object based on it for >> +that device. >> + >> +Those struct acpi_device objects are never used for binding drivers to natively >> +discoverable devices, because they are represented by other types of device >> +objects (for example, struct pci_dev for PCI devices) that are bound to by >> +device drivers (the corresponding struct acpi_device object is then used as >> +an additional source of information on the configuration of the given device). >> +Moreover, the core ACPI device enumeration code creates struct platform_device >> +objects for the majority of devices that are discovered and enumerated with the >> +help of the platform firmware and those platform device objects can be bound to >> +by platform drivers in direct analogy with the natively enumerable devices >> +case. Therefore it is logically inconsistent and so generally invalid to bind >> +drivers to struct acpi_device objects, including drivers for devices that are >> +discovered with the help of the platform firmware. >> + >> +Historically, ACPI drivers that bound directly to struct acpi_device objects >> +were implemented for some devices enumerated with the help of the platform >> +firmware, but this is not recommended for any new drivers. As explained above, >> +platform device objects are created for those devices as a rule (with a few >> +exceptions that are not relevant here) and so platform drivers should be used >> +for handling them, even though the corresponding ACPI device objects are the >> +only source of device configuration information in that case. >> + >> +For every device having a corresponding struct acpi_device object, the pointer >> +to it is returned by the ACPI_COMPANION() macro, so it is always possible to >> +get to the device configuration information stored in the ACPI device object >> +this way. Accordingly, struct acpi_device can be regarded as a part of the >> +interface between the kernel and the ACPI Namespace, whereas device objects of >> +other types (for example, struct pci_dev or struct platform_device) are used >> +for interacting with the rest of the system. >> + >> DMA support >> =========== > Thanks a lot ! > Looks very good, will include this in next revision. > > Michał Aww, forgot that you can also just apply it yourself, so I can just fetch and rebase. Whichever version you prefer is fine with me :-) > >> >> >> >>
On Thu, Oct 5, 2023 at 10:39 PM Wilczynski, Michal <michal.wilczynski@intel.com> wrote: > > > > On 10/5/2023 8:28 PM, Wilczynski, Michal wrote: > > > > On 10/5/2023 7:57 PM, Rafael J. Wysocki wrote: > >> On Monday, September 25, 2023 4:48:35 PM CEST Michal Wilczynski wrote: > >>> Some devices implement ACPI driver as a way to manage devices > >>> enumerated by the ACPI. This might be confusing as a preferred way to > >>> implement a driver for devices not connected to any bus is a platform > >>> driver, as stated in the documentation. Clarify relationships between > >>> ACPI device, platform device and ACPI entries. > >>> > >>> Suggested-by: Elena Reshetova <elena.reshetova@intel.com> > >>> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> > >>> --- > >>> Documentation/firmware-guide/acpi/enumeration.rst | 13 +++++++++++++ > >>> 1 file changed, 13 insertions(+) > >>> > >>> diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst > >>> index 56d9913a3370..f56cc79a9e83 100644 > >>> --- a/Documentation/firmware-guide/acpi/enumeration.rst > >>> +++ b/Documentation/firmware-guide/acpi/enumeration.rst > >>> @@ -64,6 +64,19 @@ If the driver needs to perform more complex initialization like getting and > >>> configuring GPIOs it can get its ACPI handle and extract this information > >>> from ACPI tables. > >>> > >>> +ACPI bus > >>> +==================== > >>> + > >>> +Historically some devices not connected to any bus were represented as ACPI > >>> +devices, and had to implement ACPI driver. This is not a preferred way for new > >>> +drivers. As explained above devices not connected to any bus should implement > >>> +platform driver. ACPI device would be created during enumeration nonetheless, > >>> +and would be accessible through ACPI_COMPANION() macro, and the ACPI handle would > >>> +be accessible through ACPI_HANDLE() macro. ACPI device is meant to describe > >>> +information related to ACPI entry e.g. handle of the ACPI entry. Think - > >>> +ACPI device interfaces with the FW, and the platform device with the rest of > >>> +the system. > >>> + > >>> DMA support > >>> =========== > >> I rewrote the above entirely, so here's a new patch to replace this one: > >> > >> --- > >> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > >> Subject: [PATCH v2 2/9] ACPI: docs: enumeration: Clarify ACPI bus concepts > >> > >> In some cases, ACPI drivers are implemented as a way to manage devices > >> enumerated with the help of the platform firmware through ACPI. > >> > >> This might be confusing, since the preferred way to implement a driver > >> for a device that cannot be enumerated natively, is a platform > >> driver, as stated in the documentation. > >> > >> Clarify relationships between ACPI device objects, platform devices and > >> ACPI Namespace entries. > >> > >> Suggested-by: Elena Reshetova <elena.reshetova@intel.com> > >> Co-developed-by: Michal Wilczynski <michal.wilczynski@intel.com> > >> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> > >> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > >> --- > >> Documentation/firmware-guide/acpi/enumeration.rst | 43 ++++++++++++++++++++++ > >> 1 file changed, 43 insertions(+) > >> > >> Index: linux-pm/Documentation/firmware-guide/acpi/enumeration.rst > >> =================================================================== > >> --- linux-pm.orig/Documentation/firmware-guide/acpi/enumeration.rst > >> +++ linux-pm/Documentation/firmware-guide/acpi/enumeration.rst > >> @@ -64,6 +64,49 @@ If the driver needs to perform more comp > >> configuring GPIOs it can get its ACPI handle and extract this information > >> from ACPI tables. > >> > >> +ACPI device objects > >> +=================== > >> + > >> +Generally speaking, there are two categories of devices in a system in which > >> +ACPI is used as an interface between the platform firmware and the OS: Devices > >> +that can be discovered and enumerated natively, through a protocol defined for > >> +the specific bus that they are on (for example, configuration space in PCI), > >> +without the platform firmware assistance, and devices that need to be described > >> +by the platform firmware so that they can be discovered. Still, for any device > >> +known to the platform firmware, regardless of which category it falls into, > >> +there can be a corresponding ACPI device object in the ACPI Namespace in which > >> +case the Linux kernel will create a struct acpi_device object based on it for > >> +that device. > >> + > >> +Those struct acpi_device objects are never used for binding drivers to natively > >> +discoverable devices, because they are represented by other types of device > >> +objects (for example, struct pci_dev for PCI devices) that are bound to by > >> +device drivers (the corresponding struct acpi_device object is then used as > >> +an additional source of information on the configuration of the given device). > >> +Moreover, the core ACPI device enumeration code creates struct platform_device > >> +objects for the majority of devices that are discovered and enumerated with the > >> +help of the platform firmware and those platform device objects can be bound to > >> +by platform drivers in direct analogy with the natively enumerable devices > >> +case. Therefore it is logically inconsistent and so generally invalid to bind > >> +drivers to struct acpi_device objects, including drivers for devices that are > >> +discovered with the help of the platform firmware. > >> + > >> +Historically, ACPI drivers that bound directly to struct acpi_device objects > >> +were implemented for some devices enumerated with the help of the platform > >> +firmware, but this is not recommended for any new drivers. As explained above, > >> +platform device objects are created for those devices as a rule (with a few > >> +exceptions that are not relevant here) and so platform drivers should be used > >> +for handling them, even though the corresponding ACPI device objects are the > >> +only source of device configuration information in that case. > >> + > >> +For every device having a corresponding struct acpi_device object, the pointer > >> +to it is returned by the ACPI_COMPANION() macro, so it is always possible to > >> +get to the device configuration information stored in the ACPI device object > >> +this way. Accordingly, struct acpi_device can be regarded as a part of the > >> +interface between the kernel and the ACPI Namespace, whereas device objects of > >> +other types (for example, struct pci_dev or struct platform_device) are used > >> +for interacting with the rest of the system. > >> + > >> DMA support > >> =========== > > Thanks a lot ! > > Looks very good, will include this in next revision. > > > > Michał > > Aww, forgot that you can also just apply it yourself, so I can just fetch and > rebase. Whichever version you prefer is fine with me :-) So I went ahead and queued up my versions of patches [1-2/9]. They are present in the acpi-bus branch in linux-pm.git (based on 6.6-rc4) and in the bleeding-edge branch (I'll merge acpi-bus into linux-next next week if all goes well).
On 10/6/2023 5:36 PM, Rafael J. Wysocki wrote: > On Thu, Oct 5, 2023 at 10:39 PM Wilczynski, Michal > <michal.wilczynski@intel.com> wrote: >> >> >> On 10/5/2023 8:28 PM, Wilczynski, Michal wrote: >>> On 10/5/2023 7:57 PM, Rafael J. Wysocki wrote: >>>> On Monday, September 25, 2023 4:48:35 PM CEST Michal Wilczynski wrote: >>>>> Some devices implement ACPI driver as a way to manage devices >>>>> enumerated by the ACPI. This might be confusing as a preferred way to >>>>> implement a driver for devices not connected to any bus is a platform >>>>> driver, as stated in the documentation. Clarify relationships between >>>>> ACPI device, platform device and ACPI entries. >>>>> >>>>> Suggested-by: Elena Reshetova <elena.reshetova@intel.com> >>>>> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> >>>>> --- >>>>> Documentation/firmware-guide/acpi/enumeration.rst | 13 +++++++++++++ >>>>> 1 file changed, 13 insertions(+) >>>>> >>>>> diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst >>>>> index 56d9913a3370..f56cc79a9e83 100644 >>>>> --- a/Documentation/firmware-guide/acpi/enumeration.rst >>>>> +++ b/Documentation/firmware-guide/acpi/enumeration.rst >>>>> @@ -64,6 +64,19 @@ If the driver needs to perform more complex initialization like getting and >>>>> configuring GPIOs it can get its ACPI handle and extract this information >>>>> from ACPI tables. >>>>> >>>>> +ACPI bus >>>>> +==================== >>>>> + >>>>> +Historically some devices not connected to any bus were represented as ACPI >>>>> +devices, and had to implement ACPI driver. This is not a preferred way for new >>>>> +drivers. As explained above devices not connected to any bus should implement >>>>> +platform driver. ACPI device would be created during enumeration nonetheless, >>>>> +and would be accessible through ACPI_COMPANION() macro, and the ACPI handle would >>>>> +be accessible through ACPI_HANDLE() macro. ACPI device is meant to describe >>>>> +information related to ACPI entry e.g. handle of the ACPI entry. Think - >>>>> +ACPI device interfaces with the FW, and the platform device with the rest of >>>>> +the system. >>>>> + >>>>> DMA support >>>>> =========== >>>> I rewrote the above entirely, so here's a new patch to replace this one: >>>> >>>> --- >>>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >>>> Subject: [PATCH v2 2/9] ACPI: docs: enumeration: Clarify ACPI bus concepts >>>> >>>> In some cases, ACPI drivers are implemented as a way to manage devices >>>> enumerated with the help of the platform firmware through ACPI. >>>> >>>> This might be confusing, since the preferred way to implement a driver >>>> for a device that cannot be enumerated natively, is a platform >>>> driver, as stated in the documentation. >>>> >>>> Clarify relationships between ACPI device objects, platform devices and >>>> ACPI Namespace entries. >>>> >>>> Suggested-by: Elena Reshetova <elena.reshetova@intel.com> >>>> Co-developed-by: Michal Wilczynski <michal.wilczynski@intel.com> >>>> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> >>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >>>> --- >>>> Documentation/firmware-guide/acpi/enumeration.rst | 43 ++++++++++++++++++++++ >>>> 1 file changed, 43 insertions(+) >>>> >>>> Index: linux-pm/Documentation/firmware-guide/acpi/enumeration.rst >>>> =================================================================== >>>> --- linux-pm.orig/Documentation/firmware-guide/acpi/enumeration.rst >>>> +++ linux-pm/Documentation/firmware-guide/acpi/enumeration.rst >>>> @@ -64,6 +64,49 @@ If the driver needs to perform more comp >>>> configuring GPIOs it can get its ACPI handle and extract this information >>>> from ACPI tables. >>>> >>>> +ACPI device objects >>>> +=================== >>>> + >>>> +Generally speaking, there are two categories of devices in a system in which >>>> +ACPI is used as an interface between the platform firmware and the OS: Devices >>>> +that can be discovered and enumerated natively, through a protocol defined for >>>> +the specific bus that they are on (for example, configuration space in PCI), >>>> +without the platform firmware assistance, and devices that need to be described >>>> +by the platform firmware so that they can be discovered. Still, for any device >>>> +known to the platform firmware, regardless of which category it falls into, >>>> +there can be a corresponding ACPI device object in the ACPI Namespace in which >>>> +case the Linux kernel will create a struct acpi_device object based on it for >>>> +that device. >>>> + >>>> +Those struct acpi_device objects are never used for binding drivers to natively >>>> +discoverable devices, because they are represented by other types of device >>>> +objects (for example, struct pci_dev for PCI devices) that are bound to by >>>> +device drivers (the corresponding struct acpi_device object is then used as >>>> +an additional source of information on the configuration of the given device). >>>> +Moreover, the core ACPI device enumeration code creates struct platform_device >>>> +objects for the majority of devices that are discovered and enumerated with the >>>> +help of the platform firmware and those platform device objects can be bound to >>>> +by platform drivers in direct analogy with the natively enumerable devices >>>> +case. Therefore it is logically inconsistent and so generally invalid to bind >>>> +drivers to struct acpi_device objects, including drivers for devices that are >>>> +discovered with the help of the platform firmware. >>>> + >>>> +Historically, ACPI drivers that bound directly to struct acpi_device objects >>>> +were implemented for some devices enumerated with the help of the platform >>>> +firmware, but this is not recommended for any new drivers. As explained above, >>>> +platform device objects are created for those devices as a rule (with a few >>>> +exceptions that are not relevant here) and so platform drivers should be used >>>> +for handling them, even though the corresponding ACPI device objects are the >>>> +only source of device configuration information in that case. >>>> + >>>> +For every device having a corresponding struct acpi_device object, the pointer >>>> +to it is returned by the ACPI_COMPANION() macro, so it is always possible to >>>> +get to the device configuration information stored in the ACPI device object >>>> +this way. Accordingly, struct acpi_device can be regarded as a part of the >>>> +interface between the kernel and the ACPI Namespace, whereas device objects of >>>> +other types (for example, struct pci_dev or struct platform_device) are used >>>> +for interacting with the rest of the system. >>>> + >>>> DMA support >>>> =========== >>> Thanks a lot ! >>> Looks very good, will include this in next revision. >>> >>> Michał >> Aww, forgot that you can also just apply it yourself, so I can just fetch and >> rebase. Whichever version you prefer is fine with me :-) > So I went ahead and queued up my versions of patches [1-2/9]. They > are present in the acpi-bus branch in linux-pm.git (based on 6.6-rc4) > and in the bleeding-edge branch (I'll merge acpi-bus into linux-next > next week if all goes well). Thanks, great ! Will re-send the rest of the patchset. Michał >
diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst index 56d9913a3370..f56cc79a9e83 100644 --- a/Documentation/firmware-guide/acpi/enumeration.rst +++ b/Documentation/firmware-guide/acpi/enumeration.rst @@ -64,6 +64,19 @@ If the driver needs to perform more complex initialization like getting and configuring GPIOs it can get its ACPI handle and extract this information from ACPI tables. +ACPI bus +==================== + +Historically some devices not connected to any bus were represented as ACPI +devices, and had to implement ACPI driver. This is not a preferred way for new +drivers. As explained above devices not connected to any bus should implement +platform driver. ACPI device would be created during enumeration nonetheless, +and would be accessible through ACPI_COMPANION() macro, and the ACPI handle would +be accessible through ACPI_HANDLE() macro. ACPI device is meant to describe +information related to ACPI entry e.g. handle of the ACPI entry. Think - +ACPI device interfaces with the FW, and the platform device with the rest of +the system. + DMA support ===========
Some devices implement ACPI driver as a way to manage devices enumerated by the ACPI. This might be confusing as a preferred way to implement a driver for devices not connected to any bus is a platform driver, as stated in the documentation. Clarify relationships between ACPI device, platform device and ACPI entries. Suggested-by: Elena Reshetova <elena.reshetova@intel.com> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com> --- Documentation/firmware-guide/acpi/enumeration.rst | 13 +++++++++++++ 1 file changed, 13 insertions(+)