linux-kernel - Re: [PATCH] drm: bridge/dw_hdmi: Filter modes

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Message-ID: <CAD=FV=UHaUysAt3BGNXm3ULkfEJSSCsxPjDa4ZSJ4V42sSth_g@mail.gmail.com>
Date:	Thu, 18 Jun 2015 08:26:39 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Philipp Zabel <p.zabel@...gutronix.de>,
	Thierry Reding <treding@...dia.com>,
	Heiko Stuebner <heiko@...ech.de>,
	David Airlie <airlied@...ux.ie>,
	Andy Yan <andy.yan@...k-chips.com>,
	Yakir Yang <ykk@...k-chips.com>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm: bridge/dw_hdmi: Filter modes > 165MHz for DVI

Russell,

On Thu, Jun 18, 2015 at 1:53 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
>> OK, so clearly my patch won't work against mainline.  I guess it's a
>> good thing that I pointed out that it was only tested locally (would
>> have been better to test against mainline, but I don't think that's so
>> easy since there are several unlanded patches in mainline for
>> Rockchip).
>
> As far as I'm aware, Freescale's original BSP version was the same, as is
> their later BSPs, and Jon's maintained 3.14-stable kernel.

Was "the same"?  You mean was untested, or was 3.14?  It is probably
not the same "3.14 with backports" that I'm testing on, which includes
backports + things from the mailing list that haven't landed yet, as
many of the unlanded patches are things that make Rockchip HDMI work
more correctly.  Perhaps I should have called my tree "3.14 with
backports + unlanded patches" or "the chromeos 3.14 tree" to make it
clearer.

In general I haven't been posting patches that I've made to HDMI since
it appears that our tree has significant differences from mainline.
In this case the function I was touching looked identical to mainline
so I figured posting a patch seemed reasonable.

>> As pointed out by others at <http://crosreview.com/278255>, locally
>> our kernel has a slightly older version of
>> <https://lkml.org/lkml/2015/2/28/291>, which would change mdvi to be
>> as needed.
>
> Please don't post unreliable lkml.org URLs, please use some other archive
> site.  I can't access this URL at the moment.

Perhaps you can try <https://patchwork.kernel.org/patch/5906771/>

>> ...so I guess my change is blocked on someone reviewing/landing that
>> series.  If that series is rejected (or is changed sufficiently so
>> that mdvi no longer is set via drm_detect_hdmi_monitor() then my patch
>> will need to be re-spun.
>
> That's not what I said.  I said mdvi is set according to whether the mode
> being set is a CEA mode or not.

Perhaps now that you can access the patch with the patchwork link you
can re-read my email.  If/when that patch lands then mdvi _will_ be
set as per drm_detect_hdmi_monitor().

> A thought occurs to me this morning though: what happens if you connect
> a DVI monitor to an AV receiver which is then connected to this device.
> Does the resulting EDID contain the HDMI vendor ID?  If it does, it
> means that drm_detect_hdmi_monitor() will return true, indicating that
> the connected device is HDMI, and we will still allow modes greater than
> 165MHz.

I am nowhere near an HDMI expert.  If you have a better suggestion
then I'm more than happy for you to post it and drop my patch.  In my
non-expert opinion, it would seem awfully strange for an AV receiver
to modify the EDID though unless it was actively interpreting the
signal and generating a whole new signal on the other end.  In any
case, perhaps you can find such a device and that will give insight to
how we should deal with it.  Until such a device is found, it seems
fruitless to speculate.

Personally, I was pointed at "drivers/gpu/drm/i915/intel_hdmi.c".  If
you look there you will find a similar bit of code.

To summarize: I am not planning to spin my patch.  I am hopeful that
folks could review Yakir's series.  Would it help if he re-sent it
with different people in the "To" line?

Maybe when Yakir spins his series next he can include my patch?

-Doug
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