First test I could make, patching the usbaudio.c source from ubuntu 10.04 with your patch.
Now the device can play sounds at 48kHz on the Plantronics C720.
However, I can't play sounds at 16kHz anymore, I get clicks instead (exactly like it was previously when trying to play 48kHz sounds with the device set to 16kHz).
I use aplay -D hw:1,0 to run the tests (bypassing pulse etc)

I'll make further tests when I can and keep you posted.


- Yves

On 23/04/2013 13:29, Yves G wrote:
On 23/04/2013 13:24, Daniel Mack wrote:
On 23.04.2013 13:19, Yves G wrote:
On 23/04/2013 13:14, Daniel Mack wrote:
On 23.04.2013 13:07, Yves G wrote:

I'll forward that to my contacts at Plantronics
Fixing the firmware is certainly the right thing to do, but I'd
appreciate if you could still test my patch, so we can take it to the
mainline kernel. As Torstein said - there are more devices out there
which get this wrong, and I'd like to fix all of them at once.

It is my plan to do it today or tomorrow.
I'll tell you the results.

BTW: The patch does not work with the version of Alsa shipped with
Ubuntu 10.04. In that version, this is usbaudio.c that must be patched,
not stream.c.
Then the kernel they ship is ancient.
Yes. 2.6.32-46-108.
This is an old version of Ubuntu, but this is what is used as the OS of the devices I must support.
But I guess that it can be made available only with the latest version
of Alsa (which then may not work with older systems...)
Don't bother with separate version of the kernel and ALSA. Just follow
the instructions on this page and build a completely new kernel:

You should apply my patch after you completed step 7, with "git apply
I'll try that too.
For my current issue, however, I should be able to provide a fix that does not need a new/rebuilt kernel. So I'll also test a patched snd-usb-audio module.


- Yves
Best regards,