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

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Message-ID: <5547696D.8000300@gmail.com>
Date:	Mon, 04 May 2015 21:43:25 +0900
From:	Krzysztof Kozlowski <k.kozlowski.k@...il.com>
To:	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

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. It does not really
need FIMD. Using ifdefs in headers is not uncommon - many core
subsystems do this that way to provide stubs.

Probably the cleanest way would be to provide by FIMD and DECON a common
interface for DP for such operation, something like:
struct exynos_drm_crtc {
	struct drm_crtc                 base;
	...
	void (*clock_enable)(struct exynos_drm_crtc *crtc, bool enable)
);

which, if non-NULL, will be called by exynos_dp_core.c:
static void exynos_dp_poweron(struct exynos_dp_device *dp)
{
	...
	if (crtc->clock_enable)
		crtc->clock_enable(crtc, true);
}

What do you think?

Best regards,
Krzysztof
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