ALSA: usb-audio: Limit max buffer and period sizes per time
In the previous fix, we increased the max buffer bytes from 1MB to 4MB so that we can use bigger buffers for the modern HiFi devices with higher rates, more channels and wider formats. OTOH, extending this has a concern that too big buffer is allowed for the lower rates, less channels and narrower formats; when an application tries to allocate as big buffer as possible, it'll lead to unexpectedly too huge size. Also, we had a problem about the inconsistent max buffer and period bytes for the implicit feedback mode when both streams have different channels. This was fixed by the (relatively complex) patch to reduce the max buffer and period bytes accordingly. This is an alternative fix for those, a patch to kill two birds with one stone (*): instead of increasing the max buffer bytes blindly and applying the reduction per channels, we simply use the hw constraints for the buffer and period "time". Meanwhile the max buffer and period bytes are set unlimited instead. Since the inconsistency of buffer (and period) bytes comes from the difference of the channels in the tied streams, as long as we care only about the buffer (and period) time, it doesn't matter; the buffer time is same for different channels, although we still allow higher buffer size. Similarly, this will allow more buffer bytes for HiFi devices while it also keeps the reasonable size for the legacy devices, too. As of this patch, the max period and buffer time are set to 1 and 2 seconds, which should be large enough for all possible use cases. (*) No animals were harmed in the making of this patch. Fixes: 98c27add ("ALSA: usb-audio: Cap upper limits of buffer/period bytes for implicit fb") Fixes: fee2ec8c ("ALSA: usb-audio: Increase max buffer size") Link: https://lore.kernel.org/r/20220412130740.18933-1-tiwai@suse.de Signed-off-by:Takashi Iwai <tiwai@suse.de>
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