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From:   Enric Balletbo Serra <eballetbo@gmail.com>
Date:   Fri, 16 Feb 2018 13:34:49 +0100
Message-ID: <CAFqH_50OxDDfXjGPyNgtyu-qFn3zGqrLYprLtPJyHDYRDEczGQ@mail.gmail.com>
Subject: Re: [PATCH v3 33/43] drm/panel: simple: Change mode for Sharp lq123p1jx31
To:     Doug Anderson <dianders@chromium.org>
Cc:     Sean Paul <seanpaul@chromium.org>, Haixia Shi <hshi@chromium.org>,
        Thierry Escande <thierry.escande@collabora.com>,
        Lin Huang <hl@rock-chips.com>, David Airlie <airlied@linux.ie>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Tomasz Figa <tfiga@chromium.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Yakir Yang <ykk@rock-chips.com>,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        =?UTF-8?Q?=C3=98rjan_Eide?= <orjan.eide@arm.com>,
        Mark Yao <mark.yao@rock-chips.com>,
        Zain Wang <wzz@rock-chips.com>
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Hi,

2018-01-31 17:52 GMT+01:00 Doug Anderson <dianders@chromium.org>:
> Hi,
>
>
> On Wed, Jan 31, 2018 at 7:16 AM, Sean Paul <seanpaul@chromium.org> wrote:
>> On Wed, Jan 31, 2018 at 7:54 AM, Lucas Stach <l.stach@pengutronix.de> wrote:
>>> Am Dienstag, den 30.01.2018, 21:29 +0100 schrieb Thierry Escande:
>>>> From: Sean Paul <seanpaul@chromium.org>
>>>>
>>>> Change the mode for Sharp lq123p1jx31 panel to something more
>>>> rockchip-friendly such that we can use the fixed PLLs to
>>>> generate the pixel clock
>>>
>>> This should really switch to a display timing instead of exposing a
>>> single mode. The display timing has min, typical, max tuples for all
>>> the timings values, which would allow the attached driver to vary the
>>> timings inside the allowed bounds if it makes sense.
>>>
>>> Trying to hit a specific pixel clock to free up a PLL is exactly one of
>>> the use cases envisioned for the display timings stuff.
>>>
>>
>> Agreed, I think we had this discussion the first time around. We
>> should drop this patch.
>>
>> Thanks for catching this!
>
> Are you sure we should drop this?  In order for things to work
> properly (not generate noise on the digitizer or other EMI), this
> needs to run at a very specific pixel clock with very specific
> blanking times.  I know that earlier we had slightly different
> blanking times and Samsung came back and said that there was noise on
> the digitizer.  I could be wrong, but I don't think there's any way
> currently to be able to specify exactly what timings should be used on
> a particular board.
>
> Don't get be wrong--I think a patch such as this one that claims a
> single board's timings as the "right" ones for a generic panel is a
> bit of a hack.  ...but at the same time there are no other users of
> this panel (that I know of) in mainline and the timings presented here
> are certainly sane timings for this panel.
>
> In any case, previous discussion at: https://patchwork.kernel.org/patch/9614603/
>
>
> ...oh, and looking at the previous discussion reminds me that the
> timings presented in this here patch are actually not the right ones
> (they have the right PLL, but the wrong blankings to avoid the noise
> issues).  See <//chromium-review.googlesource.com/381015>
>

As Thierry no longer has the hardware to test these patch series, I'll
take care of these and follow the upstreaming process. I think that
doesn't make sense send a v4 version of all 43 patches for this
change. Right now, only this patch received comments so I'll wait a
bit more for if we can get the other patches reviewed. If the others
are fine just and I don't need to send a new version just don't apply
this one and I will send a second version of that specific patch. Or
even better, is really trivial what needs to be changed, so maybe the
maintainer can do it? ;)

Regards,
 Enric

>
>
> -Doug
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