Re: [PATCH v2 1/2] drm: Add a drm_drv_enabled() to check if drivers should be enabled

From: Jani Nikula <jani.nikula@linux.intel.com>
To: Sam Ravnborg <sam@ravnborg.org>,
	Javier Martinez Canillas <javierm@redhat.com>
Cc: "David Airlie" <airlied@linux.ie>,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>,
	dri-devel@lists.freedesktop.org,
	"Gurchetan Singh" <gurchetansingh@chromium.org>,
	"Dave Airlie" <airlied@redhat.com>,
	amd-gfx@lists.freedesktop.org,
	"VMware Graphics" <linux-graphics-maintainer@vmware.com>,
	"Peter Robinson" <pbrobinson@gmail.com>,
	nouveau@lists.freedesktop.org, spice-devel@lists.freedesktop.org,
	intel-gfx@lists.freedesktop.org,
	"Ben Skeggs" <bskeggs@redhat.com>,
	"Michel Dänzer" <michel@daenzer.net>,
	"Hans de Goede" <hdegoede@redhat.com>,
	"Rodrigo Vivi" <rodrigo.vivi@intel.com>,
	virtualization@lists.linux-foundation.org,
	"Pekka Paalanen" <pekka.paalanen@collabora.com>,
	"Pan, Xinhui" <Xinhui.Pan@amd.com>,
	linux-kernel@vger.kernel.org,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Christian König" <christian.koenig@amd.com>
Subject: Re: [PATCH v2 1/2] drm: Add a drm_drv_enabled() to check if drivers should be enabled
Date: Thu, 04 Nov 2021 21:54:32 +0200	[thread overview]
Message-ID: <87lf23ae87.fsf@intel.com> (raw)
In-Reply-To: <YYQ0doL/F3ULjXyr@ravnborg.org>

On Thu, 04 Nov 2021, Sam Ravnborg <sam@ravnborg.org> wrote:
> Hi Javier,
>
>> 
>> >>>  
>> >>> -	if (vgacon_text_force() && i915_modparams.modeset == -1)
>> >>> +	ret = drm_drv_enabled(&driver);
>> >>
>> >> You pass the local driver variable here - which looks wrong as this is
>> >> not the same as the driver variable declared in another file.
>> >
>> 
>> Yes, Jani mentioned it already. I got confused and thought that the driver
>> variable was also defined in the same compilation unit...
>> 
>> Maybe I could squash the following change?
>> 
>> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
>> index b18a250e5d2e..b8f399b76363 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.c
>> +++ b/drivers/gpu/drm/i915/i915_drv.c
>> @@ -89,7 +89,7 @@
>>  #include "intel_region_ttm.h"
>>  #include "vlv_suspend.h"
>>  
>> -static const struct drm_driver driver;
>> +const struct drm_driver driver;
> No, variables with such a generic name will clash.
>
> Just add a
> const drm_driver * i915_drm_driver(void)
> {
> 	return &driver;
> }
>
> And then use this function to access the drm_driver variable.

Agreed on the general principle of exposing interfaces over data.

But... why? I'm still at a loss what problem this solves. We pass
&driver to exactly one place, devm_drm_dev_alloc(), and it's neatly
hidden away.

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Graphics Center
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