linux-kernel - Re: [PATCH] drm/pl111: add ARM

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Message-ID: <CAJKOXPeweaJxUHM=uURarbW8dWeZ=PHt7W7k0wt-cfhz0_2QUg@mail.gmail.com>
Date:   Tue, 23 May 2017 13:17:18 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Eric Anholt <eric@...olt.net>, David Airlie <airlied@...ux.ie>,
        Kukjin Kim <kgene@...nel.org>,
        Colin Ian King <colin.king@...onical.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm/pl111: add ARM_AMBA dependency

On Mon, May 22, 2017 at 11:37 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Mon, May 22, 2017 at 6:32 PM, Krzysztof Kozlowski <krzk@...nel.org> wrote:
>> On Mon, May 22, 2017 at 05:20:08PM +0200, Arnd Bergmann wrote:
>>> The driver is written in a way to enable compile-testing without CONFIG_ARM_AMBA,
>>> but it just causes needless warnings:
>>>
>>> drivers/gpu/drm/pl111/pl111_drv.c:149:26: error: 'pl111_drm_driver' defined but not used [-Werror=unused-variable]
>>> drivers/gpu/drm/pl111/pl111_drv.c:81:12: error: 'pl111_modeset_init' defined but not used [-Werror=unused-function]
>>>
>>> This removes the #ifdef instead, and adds a dependency on ARM_AMBA to
>>> only let us build the driver when the base support is enabled.
>>>
>>> Unfortunately, this requires removing one redundant 'select ARM_AMBA'
>>> line from mach-s3c64xx to avoid a circular dependency.
>>>
>>> It might be good to allow manually enabling ARM_AMBA when COMPILE_TEST
>>> is turned on, but that should be a separate patch and may cause other
>>> build regressions.
>>>
>>> Fixes: bed41005e617 ("drm/pl111: Initial drm/kms driver for pl111")
>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>> ---
>>>  arch/arm/mach-s3c64xx/Kconfig     | 1 -
>>>  drivers/gpu/drm/pl111/Kconfig     | 1 +
>>>  drivers/gpu/drm/pl111/pl111_drv.c | 2 --
>>>  3 files changed, 1 insertion(+), 3 deletions(-)
>>>
>>> diff --git a/arch/arm/mach-s3c64xx/Kconfig b/arch/arm/mach-s3c64xx/Kconfig
>>> index 459214fa20b4..5ee5ad74a3d6 100644
>>> --- a/arch/arm/mach-s3c64xx/Kconfig
>>> +++ b/arch/arm/mach-s3c64xx/Kconfig
>>> @@ -40,7 +40,6 @@ config CPU_S3C6410
>>>
>>>  config S3C64XX_PL080
>>>       def_bool DMADEVICES
>>> -     select ARM_AMBA
>>
>> I must admit that I miss how pl111 DRM driver create circular dependency
>> with S3C64XX_PL080 (or AMBA_PL08X?). Maybe it is unrelated change and
>> should be a separate patch?
>
> When I add 'depends on ARM_AMBA' for pl111, I get this dependency loop:
>
> drivers/i2c/Kconfig:7: symbol I2C is selected by FB_DDC
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/video/fbdev/Kconfig:63: symbol FB_DDC is selected by FB_CYBER2000_DDC
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/video/fbdev/Kconfig:381: symbol FB_CYBER2000_DDC depends on FB_CYBER2000
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/video/fbdev/Kconfig:369: symbol FB_CYBER2000 depends on FB
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/video/fbdev/Kconfig:5: symbol FB is selected by DRM_KMS_FB_HELPER
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/gpu/drm/Kconfig:72: symbol DRM_KMS_FB_HELPER is selected by
> DRM_KMS_CMA_HELPER
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/gpu/drm/Kconfig:137: symbol DRM_KMS_CMA_HELPER is selected by DRM_PL111
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/gpu/drm/pl111/Kconfig:1: symbol DRM_PL111 depends on ARM_AMBA
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/amba/Kconfig:1: symbol ARM_AMBA is selected by S3C64XX_PL080
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> arch/arm/mach-s3c64xx/Kconfig:42: symbol S3C64XX_PL080 default value
> contains DMADEVICES
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> drivers/dma/Kconfig:5: symbol DMADEVICES is selected by SND_SOC_SH4_SIU
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> sound/soc/sh/Kconfig:29: symbol SND_SOC_SH4_SIU is selected by SND_SIU_MIGOR
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
> sound/soc/sh/Kconfig:59: symbol SND_SIU_MIGOR depends on I2C
>
> We could break the loop at any of those places, but the
> S3C64XX_PL080 symbol seemed the easiest way since the
> 'select' there is completely unnecessary and it directly relates
> to the change I made in PL111.

Assuming ARM_AMBA is unnecessary here, then it should be unnecessary
in other platforms as well but we have it (git grep 'select
ARM_AMBA'). The ARM_AMBA is a dependency of AMBA_PL08X which is
selected by S3C64xx... so IMHO this is needed.

Best regards,
Krzysztof