linux-kernel - Re: [PATCH 9/9] drm/bridge: ti-sn65dsi86: Skip non-standard DP rates

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Date:   Fri, 13 Dec 2019 16:47:57 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Rob Clark <robdclark@...omium.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Sean Paul <seanpaul@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jonas Karlman <jonas@...boo.se>,
        LKML <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Cc:     Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 9/9] drm/bridge: ti-sn65dsi86: Skip non-standard DP rates

Hi,

On Fri, Dec 13, 2019 at 4:07 PM Daniel Vetter <daniel@...ll.ch> wrote:
>
> On Fri, Dec 13, 2019 at 03:45:30PM -0800, Douglas Anderson wrote:
> > The bridge chip supports these DP rates according to TI's spec:
> > * 1.62 Gbps (RBR)
> > * 2.16 Gbps
> > * 2.43 Gbps
> > * 2.7 Gbps (HBR)
> > * 3.24 Gbps
> > * 4.32 Gbps
> > * 5.4 Gbps (HBR2)
> >
> > As far as I can tell, only RBR, HBR, and HBR2 are part of the DP spec.
> > If other rates work then I believe it's because the sink has allowed
> > bending the spec a little bit.
>
> I think you need to look at the eDP spec. And filter this stuff correctly
> (there's more fields there for these somewhat irky edp timings). Simply
> not using them works, but it's defeating the point of having these
> intermediate clocks for edp panels.

Ah, I see my problem.  I had earlier only found the eDP 1.3 spec which
doesn't mention these rates.  The eDP 1.4 spec does, however.  ...and
the change log for 1.4 specifically mentions that it added 4 new link
rates and also adds the "SUPPORTED_LINK_RATES" register.

I can try to spin a v2 but for now I'll hold off for additional feedback.

I'll also note that I'd be totally OK if just the first 8 patches in
this series landed for now and someone could eventually figure out how
to make this work.  With just the first 8 patches I think we will
still be in an improved state compared to where we were before (and it
fixes the panel I care about) and someone could later write the code
to skip unsupported rates...

-Doug