linux-kernel - Re: [RFC PATCH] drm/aperture: Add param to disable conflicting framebuffers removal

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Date:   Fri, 22 Oct 2021 22:12:57 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Peter Robinson <pbrobinson@...il.com>,
        Neal Gompa <ngompa13@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH] drm/aperture: Add param to disable conflicting
 framebuffers removal

On Fri, Oct 22, 2021 at 04:40:40PM +0200, Javier Martinez Canillas wrote:
> The simpledrm driver allows to use the frame buffer that was set-up by the
> firmware. This gives early video output before the platform DRM driver is
> probed and takes over.
> 
> But it would be useful to have a way to disable this take over by the real
> DRM drivers. For example, there may be bugs in the DRM drivers that could
> cause the display output to not work correctly.
> 
> For those cases, it would be good to keep the simpledrm driver instead and
> at least get a working display as set-up by the firmware.
> 
> Let's add a drm.remove_fb boolean kernel command line parameter, that when
> set to false will prevent the conflicting framebuffers to being removed.
> 
> Since the drivers call drm_aperture_remove_conflicting_framebuffers() very
> early in their probe callback, this will cause the drivers' probe to fail.

Why is that better than just modprobe.blacklisting those drivers?

-- 
Ville Syrjälä
Intel