| Message ID | 20171107104010.2884193-1-arnd@arndb.de |
|---|---|
| State | Accepted |
| Commit | 15081e85cca45e495144eb0c108926e629fde486 |
| Headers | show |
| Series | [1/2] usbip: fix off-by-one frame number calculation | expand |
On 11/07/2017 11:39 AM, Arnd Bergmann wrote: > vgadget_get_frame returns a frame number from 0 to 2046, which > may require an expensive division operation to wrap at one lower > than the usual number. > > I can't see any reason for this, and all other drivers wrap at > a power-of-two number. My best explanation is that it was a simple > typo, so I'm changing the % modulo operator into a cheaper bitmask > that the other drivers use, to make it wrap after 0x7ff rather than > before it. > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> Looks good to me: Reviewed-by: Krzysztof Opasiak <k.opasiak@samsung.com> -- Krzysztof Opasiak Samsung R&D Institute Poland Samsung Electronics
On 11/07/2017 04:21 AM, Krzysztof Opasiak wrote: > > > On 11/07/2017 11:39 AM, Arnd Bergmann wrote: >> vgadget_get_frame returns a frame number from 0 to 2046, which >> may require an expensive division operation to wrap at one lower >> than the usual number. >> >> I can't see any reason for this, and all other drivers wrap at >> a power-of-two number. My best explanation is that it was a simple >> typo, so I'm changing the % modulo operator into a cheaper bitmask >> that the other drivers use, to make it wrap after 0x7ff rather than >> before it. >> >> Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > Looks good to me: > Reviewed-by: Krzysztof Opasiak <k.opasiak@samsung.com> > Acked-by: Shuah Khan <shuahkh@osg.samsung.com> thanks, -- Shuah
diff --git a/drivers/usb/usbip/vudc_dev.c b/drivers/usb/usbip/vudc_dev.c index 0c07348820ea..16fb4f85a6f6 100644 --- a/drivers/usb/usbip/vudc_dev.c +++ b/drivers/usb/usbip/vudc_dev.c @@ -145,7 +145,7 @@ static int vgadget_get_frame(struct usb_gadget *_gadget) do_gettimeofday(&now); return ((now.tv_sec - udc->start_time.tv_sec) * 1000 + (now.tv_usec - udc->start_time.tv_usec) / 1000) - % 0x7FF; + & 0x7FF; } static int vgadget_set_selfpowered(struct usb_gadget *_gadget, int value)
vgadget_get_frame returns a frame number from 0 to 2046, which may require an expensive division operation to wrap at one lower than the usual number. I can't see any reason for this, and all other drivers wrap at a power-of-two number. My best explanation is that it was a simple typo, so I'm changing the % modulo operator into a cheaper bitmask that the other drivers use, to make it wrap after 0x7ff rather than before it. Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- drivers/usb/usbip/vudc_dev.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 2.9.0