Re: [PATCH v1] media: uvcvideo: handle urb completion in a work queue

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Alan,

On Wednesday 09 September 2015 11:14:38 Alan Stern wrote:
> On Wed, 9 Sep 2015, Laurent Pinchart wrote:
> > On Wednesday 09 September 2015 10:30:12 Hans de Goede wrote:
> >> On 08-09-15 16:36, Alan Stern wrote:
> >>> On Tue, 8 Sep 2015, Hans de Goede wrote:
> >>>> On 09/07/2015 06:23 PM, Mian Yousaf Kaukab wrote:
> >>>>> urb completion callback is executed in host controllers interrupt
> >>>>> context. To keep preempt disable time short, add urbs to a list on
> >>>>> completion and schedule work to process the list.
> >>>>> 
> >>>>> Moreover, save timestamp and sof number in the urb completion
> >>>>> callback to avoid any delays.
> >>>> 
> >>>> Erm, I thought that we had already moved to using threaded interrupt
> >>>> handling for the urb completion a while (1-2 years ?) back. Is this
> >>>> then still needed ?
> >>> 
> >>> We moved to handling URB completions in a tasklet, not a threaded
> >>> handler.
> >> 
> >> Right.
> >> 
> >>> (Similar idea, though.)  And the change was made in only one
> >>> or two HCDs, not in all of them.
> >> 
> >> Ah, I was under the impression this was a core change, not a per
> >> hcd change.
> > 
> > Instead of fixing the issue in the uvcvideo driver, would it then make
> > more sense to fix it in the remaining hcd drivers ?
> 
> Unfortunately that's not so easy.  It involves some subtle changes
> related to the way isochronous endpoints are handled.  I wouldn't know
> what to change in any of the HCDs, except the ones that I maintain.

I'm not saying it would be easy, but I'm wondering whether it makes change to 
move individual USB device drivers to work queues when the long term goal is 
to use tasklets for URB completion anyway.

-- 
Regards,

Laurent Pinchart