Re: [PATCH v3 6/6] arm64: dts: rockchip: Specify override mode for kevin panel

From: "Stéphane Marchesin" <marcheu@chromium.org>
To: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org,
	Jeffy Chen <jeffy.chen@rock-chips.com>,
	Emil Renner Berthing <kernel@esmil.dk>,
	Arnd Bergmann <arnd@arndb.de>,
	Tomeu Vizoso <tomeu.vizoso@collabora.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Brian Norris <briannorris@chromium.org>,
	Will Deacon <will.deacon@arm.com>,
	Doug Anderson <dianders@chromium.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	Rob Herring <robh+dt@kernel.org>,
	enric.balletbo@collabora.co.uk,
	Thierry Reding <thierry.reding@gmail.com>,
	"Kristian H. Kristensen" <hoegsberg@chromium.org>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Matthias Kaehlcke <mka@chromium.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3 6/6] arm64: dts: rockchip: Specify override mode for kevin panel
Date: Tue, 24 Apr 2018 16:02:26 -0700	[thread overview]
Message-ID: <CADMs+9a+dwKeKUDHYeiUON6q1UOnt84HoJ4bpjT=6aYm7OZG9A@mail.gmail.com> (raw)
In-Reply-To: <CAAEAJfAQMzUfM86o-xNoyBQzTiEMNH+W=9FyFpBy99nA3HrVgw@mail.gmail.com>

On Tue, Apr 24, 2018 at 7:31 AM, Ezequiel Garcia
<ezequiel@vanguardiasur.com.ar> wrote:
> Hi Doug, Sean:
>
> I would like to move this forward.
>
> On 26 February 2018 at 15:23, Doug Anderson <dianders@chromium.org> wrote:
>> Hi,
>>
>> On Thu, Feb 8, 2018 at 9:48 AM, Sean Paul <seanpaul@chromium.org> wrote:
>>> This patch adds an override mode for kevin devices. The mode increases
>>> both back porches to allow a pixel clock of 26666kHz as opposed to the
>>> 'typical' value of 252750kHz. This is needed to avoid interference with
>>> the touch digitizer on these laptops.
>>>
>>> Changes in v2:
>>>  - Wrap the timing in display-timings node to match binding (Rob/Thierry)
>>> Changes in v3:
>>>  - Unwrap the timing from display-timings and rename panel-timing (Rob)
>>>
>>> Cc: Doug Anderson <dianders@chromium.org>
>>> Cc: Eric Anholt <eric@anholt.net>
>>> Cc: Heiko Stuebner <heiko@sntech.de>
>>> Cc: Jeffy Chen <jeffy.chen@rock-chips.com>
>>> Cc: Rob Herring <robh+dt@kernel.org>
>>> Cc: Stéphane Marchesin <marcheu@chromium.org>
>>> Cc: Thierry Reding <thierry.reding@gmail.com>
>>> Cc: devicetree@vger.kernel.org
>>> Cc: dri-devel@lists.freedesktop.org
>>> Cc: linux-rockchip@lists.infradead.org
>>> Signed-off-by: Sean Paul <seanpaul@chromium.org>
>>> ---
>>>  arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts | 14 ++++++++++++++
>>>  1 file changed, 14 insertions(+)
>>>
>>> diff --git a/arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts b/arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts
>>> index 191a6bcb1704..658411ce37ea 100644
>>> --- a/arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts
>>> +++ b/arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts
>>> @@ -98,6 +98,20 @@
>>>                 backlight = <&backlight>;
>>>                 power-supply = <&pp3300_disp>;
>>>
>>> +               panel-timing {
>>> +                       clock-frequency = <266604720>;
>>> +                       hactive = <2400>;
>>> +                       hfront-porch = <48>;
>>> +                       hback-porch = <84>;
>>> +                       hsync-len = <32>;
>>> +                       hsync-active = <0>;
>>> +                       vactive = <1600>;
>>> +                       vfront-porch = <3>;
>>> +                       vback-porch = <120>;
>>> +                       vsync-len = <10>;
>>> +                       vsync-active = <0>;
>>> +               };
>>> +
>>>                 ports {
>>>                         panel_in_edp: endpoint {
>>>                                 remote-endpoint = <&edp_out_panel>;
>>
>> Kristian brought an old bug to my attention
>> <https://bugs.chromium.org/p/chromium/issues/detail?id=750354> and it
>> made me think.  Should we somehow adjust the bindings here to account
>> for the fact that a board may source several different panels?
>>
>> AKA: on some boards an ODM may want to second source (or third source,
>> or ...) the panel.  They'll randomly connect several different panels
>> to the board and ship the boards out.  The panels are all compatible
>> electrically (same power sequencing) but might need slightly different
>> timings.  In this particular case there's no board-level strappings
>> for the different panels--it's assumed that the EDID on the panels can
>> be used to distinguish them.
>>
>> In that case it seems like it would be nice to allow specifying more
>> than one "panel-timing" nodes.  Maybe keyed off some type of ID that's
>> present in the EDID?
>>
>>
>> Is that something we'd want to account for before we land this series?
>>  It seems like it would just be adding an extra level of nodes?
>>
>
> AFAICS, there is no EDID without a DDC bus, which we don't
> seem to have on gru platforms, do we?

IIRC historically we've only done second sourcing when
doable because either:
1. the timings between all the panels we use are compatible, or
2. we have a working DDC to figure it out for us.

In other words, we haven't handled the case where timings are not
compatible and we can't address this by reading EDIDs.

Stéphane

>
> Regards,
> --
> Ezequiel García, VanguardiaSur
> www.vanguardiasur.com.ar
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