linux-kernel - Re: [PATCH] drm/exynos: Fix build breakage on !DRM_EXYNOS

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Date:	Mon, 04 May 2015 22:24:06 +0900
From:	Krzysztof Kozlowski <k.kozlowski.k@...il.com>
To:	Andrzej Hajda <a.hajda@...sung.com>,
	Daniel Stone <daniel@...ishbar.org>
CC:	Inki Dae <inki.dae@...sung.com>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Seung-Woo Kim <sw0312.kim@...sung.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Kukjin Kim <kgene@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] drm/exynos: Fix build breakage on !DRM_EXYNOS_FIMD

W dniu 04.05.2015 o 22:15, Andrzej Hajda pisze:
> Hi,
> 
> 
> On 05/04/2015 02:43 PM, Krzysztof Kozlowski wrote:
>> 2015-05-04 20:34 GMT+09:00 Daniel Stone <daniel@...ishbar.org>:
>>> Hi,
>>>
>>> On 4 May 2015 at 08:43, Inki Dae <inki.dae@...sung.com> wrote:
>>>> On 2015년 05월 02일 13:08, Krzysztof Kozlowski wrote:
>>>>> Selecting CONFIG_FB_S3C disables CONFIG_DRM_EXYNOS_FIMD leading to build
>>>>> error:
>>>>
>>>> No, eDP has no any dependency of FIMD but DECON. Just add dependency
>>>> code like below,
>>>>
>>>>  config DRM_EXYNOS7_DECON
>>>>         bool "Exynos DRM DECON"
>>>> -       depends on DRM_EXYNOS
>>>> +       depends on DRM_EXYNOS && !FB_S3C
>>
>> Actually my commit message was not detailed enough. The FB_S3C here
>> won't solve the issue because you may:
>> 1, disable FIMD and FB_S3C,
>> 2, enabke DECON and DP,
>> and it won't compile.
>>
>> Currently the FIMD must be enabled if DRM_EXYNOS_DP is enabled.
>>
>>>
>>> But it does clearly and explicitly call fimd_dp_clock_enable from
>>> exynos_dp_powero{n,ff}. So the dependency you're proposing seems
>>> backwards: it's not an expression of the requirements of the current
>>> code (that FIMD DP code be available, i.e. CONFIG_DRM_EXYNOS_FIMD is
>>> selected), but an indirect expression of another dependency
>>> (CONFIG_FB_S3C disables CONFIG_DRM_EXYNOS_FIMD, so disable
>>> CONFIG_FB_S3C).
>>>
>>> Additionally, as the call comes from exynos_dp_core.c, which is built
>>> by CONFIG_DRM_EXYNOS_DP (an explicitly user-selectable option), why
>>> shouldn't the dependency be there? Ah, because the dependency on DP is
>>> for (DECON || FIMD), but as DECON doesn't provide
>>> fimd_dp_clock_enable(), it doesn't seem like it would compile if you
>>> selected DECON and not FIMD.
>>>
>>> So, for me, the cleanest solution would be config DRM_EXYNOS_DP gains
>>> a hard dependency on DRM_EXYNOS_FIMD, at least until it can be fixed
>>> to compile without FIMD.
>>
>> Right, you correctly pointed current dependencies. Still it looks little
>> hacky because EXYNOS_DP may work with FIMD or DECON. 
> 
> Are you sure? I have not seen any chipset having DECON and DP. In all
> chipsets known to me DP is always accompanied by FIMD. I guess it can
> change in the future, but for now hard dependency on FIMD seems to be OK
> - it just reflects hardware design.
> Of course this is just my humble opinion :)

OK, so my next question would be: does DECON requires similar clock
handling like FIMD on certain SoCs? In other words - does something like
fimd_dp_clock_enable() have any sense in context of DECON?

Best regards,
Krzysztof

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