Created attachment 294219 [details]
in 5.9.11 the module works so the disrupting change must be somewhere in the 5.10 tree, attached is the kernel trace.
Problem is present in 5.10.0-rc4 but not in 5.9.15.
I can confirm that the PWC webcam is no longer working with the 5.10 kernel series (tried both 5.10.0 and 5.10.2) but, similarly, continues to work OK with 5.9.16.
The app level diagnostic I'm seeing is:
'libv4l2: error turning on stream: Cannot allocate memory
error: v4l2-helpers: unable to start stream' (from OBS)
and from systemd:
'kernel: pwc: Failed to allocate urb buffer 0'
The problem is presumably related to the changes in the DMA mapping in kernel 5.10 (commit 5a32c3413d3340f90c82c84b375ad4b335a59f28) as pwc uses noncoherent DMA buffers. Reverting commit 1161db6776bd1c35257e1e362e91bcb1b3fe4347 (which fixes performance issues) make pwc work again but opens up the orginial problem of transfer rates on armv7l.
Patch by Matwey V. Kornilov from the 4th January fixes the problem in the correct way, please consider applying it to the 5.10 as well as the 5.11 tree.
I will try this patch, because I have also the same error with my webcam "Creative Labs Webcam 5 (usb-0000:00:1d.0-2)" with kernel linux 5.10.7.
@Harald Jenny: can you provide the link to this patch, or add it as attachment with the bugreport ?
Created attachment 294633 [details]
patch for pwc courtesy of Matwey V. Kornilov
I attached the patch to this bug report hopefully it fixes your problem too.
*** Bug 211195 has been marked as a duplicate of this bug. ***
@Harald Jenny : I tested your patch, it works, my webcam works now with kernel 5.10.7,
I hope it will be applied to 5.10 and 5.11 tree.
That is very good to hear thanks goes to Matwey V. Kornilov for the fast patch.
On Thu, Jan 14, 2021 at 09:47:14PM +0000, firstname.lastname@example.org wrote:
> --- Comment #10 from Barto (email@example.com) ---
> @Harald Jenny : I tested your patch, it works, my webcam works now with
> I hope it will be applied to 5.10 and 5.11 tree.
Please read Documentation/SubmittingPatches for how to properly get a
patch accepted to the kernel. Attaching it in bugzilla does not work :)
The patch was just uploaded here to allow people to fix already released kernels, patch submitter Matwey V. Kornilov took care of submitting it for kernel inclusion. But thanks for your hint anyway :-).
So, this patch has now landed in the 5.11.1, 5.10.18, and 5.4.100 kernel branches.
I have compiled and tested the former two versions and all seems good.
Ok then I think we can close this bug.