linux-kernel - Re: [PATCH] drivers: gpu: drm: virtio: fix dependency of DRM_VIRTIO

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Date:   Tue, 22 Dec 2020 16:26:32 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     "Enrico Weigelt, metux IT consult" <info@...ux.net>
Cc:     linux-kernel@...r.kernel.org, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] drivers: gpu: drm: virtio: fix dependency of
 DRM_VIRTIO_GPU on VIRTIO

On Fri, Dec 04, 2020 at 02:12:21PM +0100, Enrico Weigelt, metux IT consult wrote:
> VIRTIO itself has no dependencies and therefore can easily be just
> select'ed, instead of depending on it. The current depends on causes
> any others trying to select VIRTIO to fail like this:
> 
>    drivers/gpu/drm/Kconfig:74:error: recursive dependency detected!
>    drivers/gpu/drm/Kconfig:74:	symbol DRM_KMS_HELPER is selected by DRM_VIRTIO_GPU
>    drivers/gpu/drm/virtio/Kconfig:2:	symbol DRM_VIRTIO_GPU depends on VIRTIO
>    drivers/virtio/Kconfig:2:	symbol VIRTIO is selected by GPIO_VIRTIO
>    drivers/gpio/Kconfig:1618:	symbol GPIO_VIRTIO depends on GPIOLIB
>    drivers/gpio/Kconfig:14:	symbol GPIOLIB is selected by I2C_MUX_LTC4306
>    drivers/i2c/muxes/Kconfig:47:	symbol I2C_MUX_LTC4306 depends on I2C
>    drivers/i2c/Kconfig:8:	symbol I2C is selected by FB_DDC
>    drivers/video/fbdev/Kconfig:63:	symbol FB_DDC depends on FB
>    drivers/video/fbdev/Kconfig:12:	symbol FB is selected by DRM_KMS_FB_HELPER
>    drivers/gpu/drm/Kconfig:80:	symbol DRM_KMS_FB_HELPER depends on DRM_KMS_HELPER
> 
> It seems that having both 'depends on' as well as 'select' on the same symbol
> sends us into big trouble, and Kconfig can't break up the circular dependency
> (note that in the tested configuration, neither I2C, FB or DRM are enabled at
> all). Perhaps we could consider this a bug in Kconfig, but the trouble can
> easily be circumvented by changing 'depends on' into 'select'.
> 
> DRM_VIRTIO_GPU also depends on VIRTIO_MENU, so even after this change, that
> option will only show up if the user already enabled virtio in the config.
> 
> This change didn't cause any changes in the .config after menuconfig run,
> so we should be completely safe here.
> 
> Signed-off-by: Enrico Weigelt, metux IT consult <info@...ux.net>

Pushed to drm-misc-next.

thanks,
  Gerd