[Intel-gfx] [PATCH] [drm][i915] Increase LSPCON timeout

[Fredrik Schön]

Shashank,

Den tors 16 aug. 2018 kl 10:15 skrev Sharma, Shashank
<shashank.sharma at intel.com>:
>
> Hey Chris,
>
>
> On 8/16/2018 1:13 PM, Chris Wilson wrote:
> > Quoting Sharma, Shashank (2018-08-16 08:33:36)
> >> Regards
> >>
> >> Shashank
> >>
> >>
> >> On 8/16/2018 12:47 PM, Jani Nikula wrote:
> >>> On Wed, 15 Aug 2018, Rodrigo Vivi <rodrigo.vivi at intel.com> wrote:
> >>>> On Wed, Aug 15, 2018 at 03:39:40PM -0700, Rodrigo Vivi wrote:
> >>>>> On Mon, Aug 13, 2018 at 07:51:33PM +0200, Fredrik Schön wrote:
> >>>>>
> >>>>> First of all we need to fix the commit subject:
> >>>>>
> >>>>> drm/i915: Increase LSPCON timeout
> >>>>>
> >>>>> (this can be done when merging, no need to resend)
> >>>>>
> >>>>>> 100 ms is not enough time for the LSPCON adapter on Intel NUC devices to
> >>>>>> settle. This causes dropped display modes at driver initialisation.
> >>>>>>
> >>>>>> Increase timeout to 1000 ms.
> >>>>>>
> >>>>>> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1570392
> >>>>> Missusage of "Fixes:" tag, please read
> >>>>>
> >>>>> https://01.org/linuxgraphics/gfx-docs/maintainer-tools/drm-intel.html#fixes
> >>>>>
> >>>>> But also no need for resending... could be fixed when merging
> >>>>>
> >>>>> The right one would be:
> >>>>>
> >>>>> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1570392
> >>>>> Fixes: 357c0ae9198a ("drm/i915/lspcon: Wait for expected LSPCON mode to settle")
> >>>>> Cc: Shashank Sharma <shashank.sharma at intel.com>
> >>>>> Cc: Imre Deak <imre.deak at intel.com>
> >>>>> Cc: Jani Nikula <jani.nikula at intel.com>
> >>>>> Cc: <stable at vger.kernel.org> # v4.11+
> >>>>>
> >>>>> Since initial 100 seemed to be empirical and this increase seems to
> >>>>> help other cases I'm in favor of this move so
> >>>>>
> >>>>> Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> >>>>>
> >>>>> However I will wait a bit before merging it
> >>>>> so Imre, Shashank, and/or Jani can take a look here...
> >>>> now, really cc'ing them...
> >>> Shashank? Does this slow down non-LSPCON paths?
> >> This will slow down the lspcon probing and resume part, but both of them
> >> happen only when LSPCON device is found. So to answer your question,
> >> this will not slow down the non-lspcon path, but will slow down the
> >> LSPCON connector resume and probe time. but I would recommend, instead
> >> of increasing it to 1000 ms in a single shot, we might want to gradually
> >> pick this up, on a wake-and-check way.
> > wait_for() checks every [10us, 1ms] until the condition is met, or it
> > times out. So, so long as we don't enter this path for !LPSCON where we
> > know that it will timeout, the wait_for() will only take as long as is
> > required for the connector to settle.
> We wont hit !LSPCON timeout case here, as we have already read the
> dongle signature successfully by now.  But I was thinking that, if the
> spec recommends max wait time as 100ms (which is of course doesn't seem
> enough), if we can't detect i2c-over-aux after first 500ms, I guess we
> wont be able to do that in next 500ms too. So is it really ok to wait
> this long in the resume sequence ?
>
> I guess Fredrik can provide some inputs here on if there are some
> experiments behind this number of 1000ms, or this is just a safe bet ?
> >

My first patch attempt - which is attached to the Redhat and FDO Bugzilla
bugs - added a retry loop around the original 100 ms timeout. The retry loop
did trigger, but never more than once in a row in my testing.

So possibly 200 ms would be a sufficient timeout, but as the wait_for() loop
terminates early on success I suggested a conservative value of 1000 ms.

> > Can we do other connectors at the same time, or does probing LSPCON
> > block the system?
> We can do other connectors at the same time in DRM layer at-least,
> LSPCON blocks only this connector. I was curious if are we doing this
> during the resume scenario or is this in the sequential get_connector()
> type of call  ?
> - Shashank
> > -Chris
/F