linux-kernel - [PATCH v2] Revert "drm/fb-helper: improve DRM fbdev emulation device names"

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Date:   Wed, 20 Oct 2021 18:57:40 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Daniel Vetter <daniel@...ll.ch>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Johannes Stezenbach <js@...21.net>,
        Javier Martinez Canillas <javierm@...hat.com>,
        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
Subject: [PATCH v2] Revert "drm/fb-helper: improve DRM fbdev emulation device names"

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
match against the fbdev names and so broke after the mentioned commit.

Since the names in /proc/fb are used by tools that consider it an uAPI,
let's restore the old names even when this lead to silly names like the
one mentioned above.

Fixes: b3484d2b03e4 ("drm/fb-helper: improve DRM fbdev emulation device names")
Reported-by: Johannes Stezenbach <js@...21.net>
Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
---

Changes in v2:
- Add a comment explaining that the current /proc/fb names are an uAPI.
- Add a Fixes: tag so it can be cherry-picked by stable kernels.
- Add Ville Syrjälä's Reviewed-by tag.

 drivers/gpu/drm/drm_fb_helper.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 8e7a124d6c5a..22bf690910b2 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1743,7 +1743,13 @@ 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",
+	/*
+	 * The DRM drivers fbdev emulation device name can be confusing if the
+	 * driver name also has a "drm" suffix on it. Leading to names such as
+	 * "simpledrmdrmfb" in /proc/fb. Unfortunately, it's an uAPI and can't
+	 * be changed due user-space tools (e.g: pm-utils) matching against it.
+	 */
+	snprintf(info->fix.id, sizeof(info->fix.id), "%sdrmfb",
 		 fb_helper->dev->driver->name);
 
 }
-- 
2.31.1