linux-kernel - Re: [PATCH] accel: work around DRM

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Message-ID: <20230127101701.GA1416485@linux.intel.com>
Date:   Fri, 27 Jan 2023 11:17:01 +0100
From:   Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Oded Gabbay <ogabbay@...nel.org>,
        Jeffrey Hugo <quic_jhugo@...cinc.com>,
        Jacek Lawrynowicz <jacek.lawrynowicz@...ux.intel.com>,
        Dave Airlie <airlied@...hat.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Melissa Wen <mwen@...lia.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel@...ts.freedesktop.org, Arnd Bergmann <arnd@...db.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] accel: work around DRM_ACCEL dependencies

Hi

On Fri, Jan 27, 2023 at 10:36:20AM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> At the moment, accel drivers can be built-in even with CONFIG_DRM=m,
> but this causes a link failure:
> 
> x86_64-linux-ld: drivers/accel/ivpu/ivpu_drv.o: in function `ivpu_dev_init':
> ivpu_drv.c:(.text+0x1535): undefined reference to `drmm_kmalloc'
> x86_64-linux-ld: ivpu_drv.c:(.text+0x1562): undefined reference to `drmm_kmalloc'
> x86_64-linux-ld: drivers/accel/ivpu/ivpu_drv.o: in function `ivpu_remove':
> ivpu_drv.c:(.text+0x1faa): undefined reference to `drm_dev_unregister'
> x86_64-linux-ld: drivers/accel/ivpu/ivpu_drv.o: in function `ivpu_probe':
> ivpu_drv.c:(.text+0x1fef): undefined reference to `__devm_drm_dev_alloc'

Ehh, this should not happen.

> This could be avoided by making DRM_ACCEL a tristate symbol, which
> would mean that every ACCEL driver is guarantee to be able to link
> against DRM as well. However, having both as =m causes another link
> failure because the DRM core code also links against the accel driver:
>
> x86_64-linux-ld: drivers/gpu/drm/drm_drv.o: in function `drm_minor_register':
> drm_drv.c:(.text+0x259): undefined reference to `accel_debugfs_init'
> x86_64-linux-ld: drm_drv.c:(.text+0x298): undefined reference to `accel_minor_replace'
> 
> I think it will be necessary to establish a link hierarchy between drm.ko
> and drm_accel.ko to avoid circular dependencies like this, but until then
> the only way that both can be used is to have both subsystems built into
> the kernel. Enforce this using a Kconfig dependency.

Hmm, it was discussed a bit before and conclusion was that accel will be
compiled in drm.ko to avoid circular dependencies. There should be
no drm_accel.ko module.

> Fixes: 8bf4889762a8 ("drivers/accel: define kconfig and register a new major")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/accel/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/accel/Kconfig b/drivers/accel/Kconfig
> index 834863902e16..dd18d3b2028c 100644
> --- a/drivers/accel/Kconfig
> +++ b/drivers/accel/Kconfig
> @@ -8,7 +8,7 @@
>  #
>  menuconfig DRM_ACCEL
>  	bool "Compute Acceleration Framework"
> -	depends on DRM
> +	depends on DRM=y

Would making ivpu Kconfig:

depends on DRM
select DRM_ACCEL

solve the problem and still allow to drm to be build as module ? 

Regards
Stanislaw