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

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Date:   Mon, 22 May 2017 23:37:56 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>
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 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.

        Arnd