Re: [PATCH] drm/i915: fix lane bandwidth capping for DP 1.2 sinks

[Imre Deak <imre.deak@intel.com>]

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On Tue, 2013-07-09 at 14:35 +0200, Daniel Vetter wrote:
> On Tue, Jul 9, 2013 at 12:40 PM, Imre Deak <imre.deak@intel.com> wrote:
> > DP 1.2 compatible displays may report a 5.4Gbps maximum bandwidth which
> > the driver will treat as an invalid value and use 1.62Gbps instead. Fix
> > this by capping to 2.7Gbps anything beyond the DP 1.1 bandwidth range.
> >
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 11eb697..c6dd61f 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -71,11 +71,16 @@ intel_dp_max_link_bw(struct intel_dp *intel_dp)
> >  {
> >         int max_link_bw = intel_dp->dpcd[DP_MAX_LINK_RATE];
> >
> > +       if (max_link_bw > DP_LINK_BW_2_7)
> > +               return DP_LINK_BW_2_7;
> > +
> >         switch (max_link_bw) {
> >         case DP_LINK_BW_1_62:
> >         case DP_LINK_BW_2_7:
> 
> Shouldn't we just add a new case for 5.4 GHz and cap it appropriately.
> As is we'll eat any bogus value > BW_2_7 ...

I thought that this is more future proof. We would add proper 5.4
support as part of a bigger 1.2 enabling work, having there a similar
capping to BW_5_4 for post DP 1.2 sinks.

> -Daniel
> 
> >                 break;
> >         default:
> > +               WARN(1, "invalid max DP link bw val %x, using 1.62Gbps\n",
> > +                    max_link_bw);
> >                 max_link_bw = DP_LINK_BW_1_62;
> >                 break;
> >         }
> > --
> > 1.8.1.2
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> 
> 
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch


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