linux-kernel - Re: [PATCH] Revert "drm/fb-helper: improve DRM fbdev emulation device names"

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Message-ID: <YWAlUBoMlerOGJEV@intel.com>
Date:   Fri, 8 Oct 2021 14:02:40 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Johannes Stezenbach <js@...21.net>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        dri-devel@...ts.freedesktop.org, Ben Skeggs <bskeggs@...hat.com>,
        nouveau@...ts.freedesktop.org
Subject: Re: [PATCH] Revert "drm/fb-helper: improve DRM fbdev emulation
 device names"

On Fri, Oct 08, 2021 at 09:17:08AM +0200, Javier Martinez Canillas wrote:
> This reverts commit b3484d2b03e4c940a9598aa841a52d69729c582a.
> 
> That change attempted to improve the DRM drivers fbdev emulation device
> names to avoid having confusing names like "simpledrmdrmfb" in /proc/fb.
> 
> But unfortunately there are user-space programs, such as pm-utils that
> query that information and so broke after the mentioned commit. Since
> the names in /proc/fb are used programs that consider it an ABI, let's
> restore the old names even when this lead to silly naming like the one
> mentioned above as an example.

The usage Johannes listed was this specificially:
 using_kms() { grep -q -E '(nouveau|drm)fb' /proc/fb; }                                                        

So it actually looks like  Daniel's
commit f243dd06180a ("drm/nouveau: Use drm_fb_helper_fill_info")
also broke the abi. But for the pm-utils use case at least
just having the "drmfb" in there should cover even nouveau.

Cc: stable@...r.kernel.org
Reviewed-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>

> 
> Reported-by: Johannes Stezenbach <js@...21.net>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---
> 
>  drivers/gpu/drm/drm_fb_helper.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 3ab07832104..8993b02e783 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1737,7 +1737,7 @@ void drm_fb_helper_fill_info(struct fb_info *info,
>  			       sizes->fb_width, sizes->fb_height);
>  
>  	info->par = fb_helper;
> -	snprintf(info->fix.id, sizeof(info->fix.id), "%s",
> +	snprintf(info->fix.id, sizeof(info->fix.id), "%sdrmfb",
>  		 fb_helper->dev->driver->name);
>  
>  }
> -- 
> 2.31.1

-- 
Ville Syrjälä
Intel