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

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Message-ID: <CAOCk7NoT9FKikk3pNi-JGZPopaicE0kM-7nEK4GeqZmEtB+nAA@mail.gmail.com>
Date:   Sun, 15 Dec 2019 18:19:06 -0700
From:   Jeffrey Hugo <jeffrey.l.hugo@...il.com>
To:     Doug Anderson <dianders@...omium.org>
Cc:     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>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 9/9] drm/bridge: ti-sn65dsi86: Skip non-standard DP rates

On Fri, Dec 13, 2019 at 5:49 PM Doug Anderson <dianders@...omium.org> wrote:
>
> 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.

Yeah, you need the eDP spec.  I previously posted
https://patchwork.kernel.org/patch/11205201/ and was hoping Bjorn
would find time to test it.  Maybe it would fit well with your series?
 I'm coming back from tracel, and hope to review everything you have,
but this caught my eye.

>
> 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