linux-kernel - Re: [PATCH 7/9] ARM: multi_v7_defconfig: Enable options for Exynos display support

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Date:	Fri, 15 May 2015 10:08:56 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Javier Martinez Canillas <javier@...hile0.org>
Cc:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	arm@...nel.org, Arnd Bergmann <arnd@...db.de>,
	Olof Johansson <olof@...om.net>,
	Kevin Hilman <khilman@...aro.org>,
	Doug Anderson <dianders@...omium.org>,
	Kukjin Kim <kgene@...nel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/9] ARM: multi_v7_defconfig: Enable options for Exynos
 display support

2015-05-15 9:58 GMT+09:00 Javier Martinez Canillas <javier@...hile0.org>:
> Hello Krzysztof,
>
> On Fri, May 15, 2015 at 2:36 AM, Krzysztof Kozlowski
> <k.kozlowski@...sung.com> wrote:
>> 2015-05-15 0:40 GMT+09:00 Javier Martinez Canillas
>> <javier.martinez@...labora.co.uk>:
>>> Many Exynos devices have devices attached to their display ports.
>>> This patch enables the needed Kconfig options to support different
>>> configuration such as simple panel, embedded DisplayPort (eDP) to
>>> LVDS bridges and HDMI displays.
>>
>> Enabling the display would be nice but for some quite long time we had
>> issues with DRM on Exynos. exynos_defconfig has it enabled and most of
>> boards boot fine with it. Exception is Arndale 5250:
>
> Yes, like I said in the other thread, the fact that Exynos DRM is
> working fine now on most boards is mostly because the bugs were
> exposed when the Exynos DRM options were enabled.

I saw your response in email 0/9 but let us stick to one thread.
So these are my only concerns - instability in the past.

>> http://storage.kernelci.org/next/next-20150514/arm-exynos_defconfig/lab-khilman/boot-exynos5250-arndale.html
>> [    1.630290] [drm:exynos_dp_bind] *ERROR* failed: of_get_videomode() : -22
>> [    1.637071] exynos-drm exynos-drm: failed to bind
>> 145b0000.dp-controller (ops exynos_dp_ops): -22
>> [    1.646504] exynos-drm exynos-drm: master bind failed: -22
>> [    1.651391] exynos-drm: probe of exynos-drm failed with error -22
>>
>
> Ajay Kumar changed the DT bindings for the Exynos DRM Display Panel
> driver some time ago but it seems that the Arndale 5250 DTS was never
> updated. Something along the lines of commit [0] is needed.

Thanks,

>
>> Anyway it is not like I am against it... just wondering. On the other
>> hand enabling it could help in early detection of errors.
>>
>
> I think that not enabling these options will just make latent bugs to
> not be exposed. As an example I found that module auto-loading was
> broken for the driver of the PTN3460 eDP to LVDS bridge used in the
> Exynos5250 Snow Chromebook and already posted a fix [1].

Right, enabling the options helps in exposing problems so they could
be spotted and fixed.


> I would had never found that bug if wouldn't had tried enabling these
> options in multi_v7 as a module. Also remember that the consumer
> version of these machines don't have a serial console so for users
> building images with multi_v7, not having display support means that
> the machine is pretty useless.

That is indeed good reason.

FWIW, I tested multi_v7 with your patches on Exynos4412 Trats2 board
and it worked fine.

Reviewed-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>

Best regards,
Krzysztof
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