linux-kernel - [PATCH] drm/fb-helper: Only reject FB changes if FB_MISC_USER

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Message-Id: <20170316095553.1586-1-michel@daenzer.net>
Date:   Thu, 16 Mar 2017 18:55:53 +0900
From:   Michel Dänzer <michel@...nzer.net>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] drm/fb-helper: Only reject FB changes if FB_MISC_USER_EVENT is set

From: Michel Dänzer <michel.daenzer@....com>

Otherwise this can also prevent modesets e.g. for switching VTs.

FB_MISC_USER_EVENT is set when the request originates from userspace,
which is what we're interested in here according to the DRM_DEBUG
output.

Bugzilla: https://bugs.freedesktop.org/99841
Fixes: 865afb11949e ("drm/fb-helper: reject any changes to the fbdev")
Signed-off-by: Michel Dänzer <michel.daenzer@....com>
---

I'm not entirely sure why the values can not match for a VT switch. If
anybody thinks this just papers over the real issue, please speak up.

 drivers/gpu/drm/drm_fb_helper.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index f6d4d9700734..9663f3b8f287 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1259,9 +1259,10 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 	 * Changes struct fb_var_screeninfo are currently not pushed back
 	 * to KMS, hence fail if different settings are requested.
 	 */
-	if (var->bits_per_pixel != fb->format->cpp[0] * 8 ||
-	    var->xres != fb->width || var->yres != fb->height ||
-	    var->xres_virtual != fb->width || var->yres_virtual != fb->height) {
+	if ((info->flags & FBINFO_MISC_USEREVENT) &&
+	    (var->bits_per_pixel != fb->format->cpp[0] * 8 ||
+	     var->xres != fb->width || var->yres != fb->height ||
+	     var->xres_virtual != fb->width || var->yres_virtual != fb->height)) {
 		DRM_DEBUG("fb userspace requested width/height/bpp different than current fb "
 			  "request %dx%d-%d (virtual %dx%d) > %dx%d-%d\n",
 			  var->xres, var->yres, var->bits_per_pixel,
-- 
2.11.0