On Tue, Jun 30, 2020 at 01:49:50PM +0300, Alexander Tsoy wrote:
В Пн, 29/06/2020 в 11:37 -0400, Sasha Levin пишет:
From: Alexander Tsoy alexander@tsoy.me
[ Upstream commit f0bd62b64016508938df9babe47f65c2c727d25c ]
For computation of the the next frame size current value of fs/fps and accumulated fractional parts of fs/fps are used, where values are stored in Q16.16 format. This is quite natural for computing frame size for asynchronous endpoints driven by explicit feedback, since in this case fs/fps is a value provided by the feedback endpoint and it's already in the Q format. If an error is accumulated over time, the device can adjust fs/fps value to prevent buffer overruns/underruns.
But for synchronous endpoints the accuracy provided by these computations is not enough. Due to accumulated error the driver periodically produces frames with incorrect size (+/- 1 audio sample).
This patch fixes this issue by implementing a different algorithm for frame size computation. It is based on accumulating of the remainders from division fs/fps and it doesn't accumulate errors over time. This new method is enabled for synchronous and adaptive playback endpoints.
Signed-off-by: Alexander Tsoy alexander@tsoy.me Link: https://lore.kernel.org/r/20200424022449.14972-1-alexander@tsoy.me Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Sasha Levin sashal@kernel.org
sound/usb/card.h | 4 ++++ sound/usb/endpoint.c | 43 ++++++++++++++++++++++++++++++++++++++--
sound/usb/endpoint.h | 1 + sound/usb/pcm.c | 2 ++ 4 files changed, 45 insertions(+), 5 deletions(-)
Please drop this patch from the queue for now (and for 4.4 as well). It introduced a regression for some devices. The fix is available, but not accepted yet.
I've dropped it from the older branches, but note that it's already in newer released stable kernels. Should it be reverted or should we wait for the fix?