| Message ID | 20180709154153.15742-2-robh@kernel.org |
|---|---|
| State | Accepted |
| Commit | 25b4e70dcce92168eab4d8113817bb4dd130ebd2 |
| Headers | show |
| Series | [v4,1/6] driver core: allow stopping deferred probe after init | expand |
On Mon, Jul 09, 2018 at 09:41:48AM -0600, Rob Herring wrote: > Deferred probe will currently wait forever on dependent devices to probe, > but sometimes a driver will never exist. It's also not always critical for > a driver to exist. Platforms can rely on default configuration from the > bootloader or reset defaults for things such as pinctrl and power domains. > This is often the case with initial platform support until various drivers > get enabled. There's at least 2 scenarios where deferred probe can render > a platform broken. Both involve using a DT which has more devices and > dependencies than the kernel supports. The 1st case is a driver may be > disabled in the kernel config. The 2nd case is the kernel version may > simply not have the dependent driver. This can happen if using a newer DT > (provided by firmware perhaps) with a stable kernel version. Deferred > probe issues can be difficult to debug especially if the console has > dependencies or userspace fails to boot to a shell. > > There are also cases like IOMMUs where only built-in drivers are > supported, so deferring probe after initcalls is not needed. The IOMMU > subsystem implemented its own mechanism to handle this using OF_DECLARE > linker sections. > > This commit adds makes ending deferred probe conditional on initcalls > being completed or a debug timeout. Subsystems or drivers may opt-in by > calling driver_deferred_probe_check_init_done() instead of > unconditionally returning -EPROBE_DEFER. They may use additional > information from DT or kernel's config to decide whether to continue to > defer probe or not. > > The timeout mechanism is intended for debug purposes and WARNs loudly. > The remaining deferred probe pending list will also be dumped after the > timeout. Not that this timeout won't work for the console which needs > to be enabled before userspace starts. However, if the console's > dependencies are resolved, then the kernel log will be printed (as > opposed to no output). So what happens if we have a set of modules which use deferred probing in order to work? For example, with sound stuff built as modules, and auto-loaded in parallel by udev, the modules get added in a random order. The modules have non-udev obvious dependencies between them (resource dependencies) which result in deferred probing being necessary to bring the device up. Eg, snd_soc_kirkwood_spdif module declares the ASoC card. snd_soc_spdif_tx is a codec as a loadable module. snd_soc_kirkwood is the CPU digital audio interface module. What I commonly see is this module load order: snd_soc_kirkwood_spdif, then snd_soc_kirkwood and then snd_soc_spdif_tx. This results at boot in: kirkwood-spdif-audio audio-subsystem: ASoC: CPU DAI kirkwood-fe not registered kirkwood-spdif-audio audio-subsystem: ASoC: CPU DAI kirkwood-fe not registered kirkwood-spdif-audio audio-subsystem: ASoC: CPU DAI kirkwood-fe not registered kirkwood-spdif-audio audio-subsystem: ASoC: CPU DAI kirkwood-fe not registered kirkwood-spdif-audio audio-subsystem: ASoC: CPU DAI kirkwood-fe not registered kirkwood-spdif-audio audio-subsystem: ASoC: CODEC DAI dit-hifi not registered kirkwood-spdif-audio audio-subsystem: ASoC: CODEC DAI dit-hifi not registered kirkwood-spdif-audio audio-subsystem: snd-soc-dummy-dai <-> kirkwood-fe mapping ok kirkwood-spdif-audio audio-subsystem: multicodec <-> kirkwood-spdif mapping ok at boot, where most of these are deferred probe attempts. So, disabling deferred probing after all the kernel-internal initcalls are run is wrong. You can have deferred probing required due to external modules, and this can kick in at any time (think about hot-pluggable hardware with a driver that's somehow componentised, like an audio device...) -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 13.8Mbps down 630kbps up According to speedtest.net: 13Mbps down 490kbps up
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index efc7aa7a0670..e83ef4648ea4 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -804,6 +804,15 @@ Defaults to the default architecture's huge page size if not specified. + deferred_probe_timeout= + [KNL] Debugging option to set a timeout in seconds for + deferred probe to give up waiting on dependencies to + probe. Only specific dependencies (subsystems or + drivers) that have opted in will be ignored. A timeout of 0 + will timeout at the end of initcalls. This option will also + dump out devices still on the deferred probe list after + retrying. + dhash_entries= [KNL] Set number of hash buckets for dentry cache. diff --git a/drivers/base/dd.c b/drivers/base/dd.c index e85705e84407..fb62f1be40d3 100644 --- a/drivers/base/dd.c +++ b/drivers/base/dd.c @@ -55,6 +55,7 @@ static LIST_HEAD(deferred_probe_pending_list); static LIST_HEAD(deferred_probe_active_list); static atomic_t deferred_trigger_count = ATOMIC_INIT(0); static struct dentry *deferred_devices; +static bool initcalls_done; /* * In some cases, like suspend to RAM or hibernation, It might be reasonable @@ -219,6 +220,51 @@ static int deferred_devs_show(struct seq_file *s, void *data) } DEFINE_SHOW_ATTRIBUTE(deferred_devs); +static int deferred_probe_timeout = -1; +static int __init deferred_probe_timeout_setup(char *str) +{ + deferred_probe_timeout = simple_strtol(str, NULL, 10); + return 1; +} +__setup("deferred_probe_timeout=", deferred_probe_timeout_setup); + +/** + * driver_deferred_probe_check_state() - Check deferred probe state + * @dev: device to check + * + * Returns -ENODEV if init is done and all built-in drivers have had a chance + * to probe (i.e. initcalls are done), -ETIMEDOUT if deferred probe debug + * timeout has expired, or -EPROBE_DEFER if none of those conditions are met. + * + * Drivers or subsystems can opt-in to calling this function instead of directly + * returning -EPROBE_DEFER. + */ +int driver_deferred_probe_check_state(struct device *dev) +{ + if (initcalls_done) { + if (!deferred_probe_timeout) { + dev_WARN(dev, "deferred probe timeout, ignoring dependency"); + return -ETIMEDOUT; + } + dev_warn(dev, "ignoring dependency for device, assuming no driver"); + return -ENODEV; + } + return -EPROBE_DEFER; +} + +static void deferred_probe_timeout_work_func(struct work_struct *work) +{ + struct device_private *private, *p; + + deferred_probe_timeout = 0; + driver_deferred_probe_trigger(); + flush_work(&deferred_probe_work); + + list_for_each_entry_safe(private, p, &deferred_probe_pending_list, deferred_probe) + dev_info(private->device, "deferred probe pending"); +} +static DECLARE_DELAYED_WORK(deferred_probe_timeout_work, deferred_probe_timeout_work_func); + /** * deferred_probe_initcall() - Enable probing of deferred devices * @@ -235,6 +281,19 @@ static int deferred_probe_initcall(void) driver_deferred_probe_trigger(); /* Sort as many dependencies as possible before exiting initcalls */ flush_work(&deferred_probe_work); + initcalls_done = true; + + /* + * Trigger deferred probe again, this time we won't defer anything + * that is optional + */ + driver_deferred_probe_trigger(); + flush_work(&deferred_probe_work); + + if (deferred_probe_timeout > 0) { + schedule_delayed_work(&deferred_probe_timeout_work, + deferred_probe_timeout * HZ); + } return 0; } late_initcall(deferred_probe_initcall); diff --git a/include/linux/device.h b/include/linux/device.h index 575c5a35ece5..d2acc78d279b 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -339,6 +339,8 @@ struct device *driver_find_device(struct device_driver *drv, struct device *start, void *data, int (*match)(struct device *dev, void *data)); +int driver_deferred_probe_check_state(struct device *dev); + /** * struct subsys_interface - interfaces to device functions * @name: name of the device function
Deferred probe will currently wait forever on dependent devices to probe, but sometimes a driver will never exist. It's also not always critical for a driver to exist. Platforms can rely on default configuration from the bootloader or reset defaults for things such as pinctrl and power domains. This is often the case with initial platform support until various drivers get enabled. There's at least 2 scenarios where deferred probe can render a platform broken. Both involve using a DT which has more devices and dependencies than the kernel supports. The 1st case is a driver may be disabled in the kernel config. The 2nd case is the kernel version may simply not have the dependent driver. This can happen if using a newer DT (provided by firmware perhaps) with a stable kernel version. Deferred probe issues can be difficult to debug especially if the console has dependencies or userspace fails to boot to a shell. There are also cases like IOMMUs where only built-in drivers are supported, so deferring probe after initcalls is not needed. The IOMMU subsystem implemented its own mechanism to handle this using OF_DECLARE linker sections. This commit adds makes ending deferred probe conditional on initcalls being completed or a debug timeout. Subsystems or drivers may opt-in by calling driver_deferred_probe_check_init_done() instead of unconditionally returning -EPROBE_DEFER. They may use additional information from DT or kernel's config to decide whether to continue to defer probe or not. The timeout mechanism is intended for debug purposes and WARNs loudly. The remaining deferred probe pending list will also be dumped after the timeout. Not that this timeout won't work for the console which needs to be enabled before userspace starts. However, if the console's dependencies are resolved, then the kernel log will be printed (as opposed to no output). Cc: Alexander Graf <agraf@suse.de> Signed-off-by: Rob Herring <robh@kernel.org> --- v4: - Rebase on driver-core-next - Only allow base 10 for timeout v3: - Merged with timeout patch. - Clarify that deferred_probe_timeout is a debug option. - Drop the 'optional' param. The only user was pinctrl, so it has to handle that functionality. - Rename function to driver_deferred_probe_check_state - Added kerneldoc for driver_deferred_probe_check_state - Print a 1 line warning if stopping deferred probe after initcalls and a WARN on timeout. .../admin-guide/kernel-parameters.txt | 9 +++ drivers/base/dd.c | 59 +++++++++++++++++++ include/linux/device.h | 2 + 3 files changed, 70 insertions(+) -- 2.17.1