[PATCH] Documentation: kernel-parameters.txt Add drm_kms_helper.poll

[Alex Deucher]

On Thu, Oct 4, 2012 at 11:28 AM, Paul Menzel
<paulepanter at users.sourceforge.net> wrote:
> Am Donnerstag, den 04.10.2012, 13:16 +0200 schrieb Daniel Vetter:
>> On Thu, Oct 4, 2012 at 12:34 PM,  <mika.kuoppala at intel.com> wrote:
>> > From: Mika Kuoppala <mika.kuoppala at intel.com>
>> >
>> > Add description for drm_kms_helper.poll module parameter introduced
>> > by commit: e58f637bb96d5a0ae0919b9998b891d1ba7e47c9
>
> Commit hashes are hard to remember. Please paste the commit summary too
> and even better add an URL so people can easily access it when not
> having a Git clone of Linux around.
>
>> > Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
>>
>> Actually I've noticed even with just hdmi it stalls for long enough to
>> miss a frame, on an otherwise idle system. Kernel testcases ftw, kms
>> locking ftl :(
>>
>> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>>
>> > ---
>> >  Documentation/kernel-parameters.txt |   11 +++++++++++
>> >  1 file changed, 11 insertions(+)
>> >
>> > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> > index f777fa9..ad97749 100644
>> > --- a/Documentation/kernel-parameters.txt
>> > +++ b/Documentation/kernel-parameters.txt
>> > @@ -741,6 +741,17 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>> >                         if its name and a colon are prepended to the EDID
>> >                         name.
>> >
>> > +       drm_kms_helper.poll=
>> > +                       Polling for connected VGA devices on older systems
>> > +                       can be quite expensive, causing latencies of
>> > +                       several hundred milliseconds. This will cause visible
>> > +                       stalls, for example in video playback. If you
>> > +                       experience stalls in display output occurring every
>> > +                       10 seconds (DRM_OUTPUT_POLL_PERIOD=(10*HZ)), disabling
>> > +                       polling might help.
>> > +                       Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
>> > +                       default: enabled
>> > +
>
> So according to Daniel the description should be updated then? For DVI
> and HDMI polling is not needed unless the connector is wired up
> incorrectly on the board? Is it right, that VGA also supports auto
> detection when everything is wired up correctly?

Legacy analog connectors don't generally support hotplug.  Most
digital displays should assuming the oem has wired up the hpd pin.
The drivers can enable polling for any connectors they want.  However,
IIRC, due to the way the hotplug and polling are handled in the common
drm code, that parameter can affect hotplug capable monitors as well.

>
> Could you also add advises what people should do? Like, if it is
> disabled people can still enable the external monitor by running ….

You can still manually check the monitor using something like xrandr.

Alex

>
>> >         dscc4.setup=    [NET]
>> >
>> >         dyndbg[="val"]          [KNL,DYNAMIC_DEBUG]
>> > --
>> > 1.7.9.5
>
> Acked-by: Paul Menzel <paulepanter at users.sourceforge.net>
>
>
> Thanks,
>
> Paul
>
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