[alsa-devel] HD-audio runtime->delay accounting

[David Henningsson]

On 09/21/2012 01:59 PM, Takashi Iwai wrote:
> Hi,
>
> recently Pierre questioned about the validity of COMBO positioning
> mode, and it turned out that the position reporting can be handled
> better if we take the difference between LPIB and DMAPOS as
> runtime->delay.  (In short, LPIB points the position where the data fed
> to the codec, and DMAPOS points the data fetched to DMA.)
>
> We cooked up a test patch below and it seems working well on a few
> machines I've tested.  I think we might have still chance to put this
> into 3.7, as this would be a good improvement.  The patch below is a
> combined work of two fixes: fixing the better stream start by always
> using SSYNC bit, and adjusting the position and runtime->delay.

Interesting. A quick question: is this affecting playback, recording, or 
both?

> Of course, the biggest question is the test coverage.
> David, could you check whether this doesn't break so much on (some)
> machines you can test?  Of course, if any other people can test it,
> it'll be a great help, too.
>
> The patch should be applied to the latest sound.git tree master
> branch, but it should be applicable (and easily resolvable) for older
> versions.

Against sound master:

patching file sound/pci/hda/hda_intel.c
Hunk #2 succeeded at 1987 (offset -17 lines).
Hunk #3 succeeded at 2012 (offset -17 lines).
Hunk #4 succeeded at 2044 (offset -17 lines).
Hunk #5 succeeded at 2144 (offset -17 lines).
Hunk #6 succeeded at 3426 (offset -104 lines).
Hunk #7 succeeded at 3490 (offset -104 lines).

> The patch extends this new mode only for recent Intel
> chips, just to be sure.

I don't think I have much such hardware here. But I've made DKMS package 
for easy testing by others. If you're running Ubuntu 12.04, you can just 
install this package, reboot, and test:

http://people.canonical.com/~diwic/temp/alsa-hda-dkms-ssync-delay_0.1_all.deb


-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic