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

[Paul Menzel]

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?

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

> >         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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