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

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Date:   Mon, 16 Dec 2019 16:31:16 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Jeffrey Hugo <jeffrey.l.hugo@...il.com>
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

Hi,

On Sun, Dec 15, 2019 at 5:19 PM Jeffrey Hugo <jeffrey.l.hugo@...il.com> wrote:
>
> 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.

Ah, interesting.  It looks like Rob has already posted a Fixup on my patch:

https://lore.kernel.org/r/20191215200632.1019065-1-robdclark@gmail.com

...that should also read the supported rates.  I need to go and review
/ test his new patch (I lost access to the hardware but should get it
back tomorrow or the next day), but would you be OK with going that
route?  I think my series is a superset of yours.  Specifically it has
these extra features atop yours:

* If link training fails and the panel supports faster rates, it will
try a faster rate in case it works.

* It adds support for using 6bpp when that's all that's needed,
reducing bandwidth to the panel (and link rate)

* It breaks things into smaller functions (assuming you agree this is
a good thing).

-Doug