Re: dvb usb issues since kernel 4.9

Hi Linus,

Em Sun, 7 Jan 2018 13:23:39 -0800
Linus Torvalds [off-list ref] escreveu:

On Sat, Jan 6, 2018 at 11:54 AM, Mauro Carvalho Chehab
[off-list ref] wrote:

quoted

Em Sat, 6 Jan 2018 16:04:16 +0100
"Josef Griebichler" [off-list ref] escreveu:  

quoted

the causing commit has been identified.
After reverting commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4cd13c21b207e80ddb1144c576500098f2d5f882
its working again.  

Just replying to me won't magically fix this. The ones that were involved on
this patch should also be c/c, plus USB people. Just added them.  

Actually, you seem to have added an odd subset of the people involved.

For example, Ingo - who actually committed that patch - wasn't on the cc.

Sorry, my fault. I forgot to add him to it.

I do think we need to simply revert that patch. It's very simple: it
has been reported to lead to actual problems for people, and we don't
fix one problem and then say "well, it fixed something else" when
something breaks.

When something breaks, we either unbreak it, or we revert the change
that caused the breakage.

It's really that simple. That's what "no regressions" means.  We don't
accept changes that cause regressions. This one did.

Yeah, we should either unbreak or revert it. In the specific case of
media devices, Alan came with a proposal of increasing the number of
buffers. This is an one line change, and increase a capture delay from
0.63 ms to 5 ms on this specific case (Digital TV) shouldn't make much
harm. So, I guess it would worth trying it before reverting the patch.

It is hard to foresee the consequences of the softirq changes for other
devices, though.

For example, we didn't have any reports about this issue affecting cameras,
Most cameras use ISOC nowadays, but some only provide bulk transfers.
We usually try to use the minimum number of buffers possible, as
increasing latency on cameras can be very annoying, specially on
videoconference applications.

Thanks,
Mauro