Re: [PATCH v2] drm/fb-helper: Fix height, width, and accel_flags in fb_var

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Thanks a lot. Pushed to drm-misc-fixes.

Am 23.05.23 um 17:06 schrieb Geert Uytterhoeven:
Fbtest contains some very simple validation of the fbdev userspace API
contract.  When used with shmob-drm, it reports the following warnings
and errors:

     height changed from 68 to 0
     height was rounded down
     width changed from 111 to 0
     width was rounded down
     accel_flags changed from 0 to 1

The first part happens because __fill_var() resets the physical
dimensions of the first connector, as filled in by drm_setup_crtcs_fb().
Fix this by retaining the original values.

The last part happens because __fill_var() forces the FB_ACCELF_TEXT
flag on, while fbtest disables all acceleration on purpose, so it can
draw safely to the frame buffer.  Fix this by setting accel_flags to
zero, as DRM does not implement any text console acceleration.
Note that this issue can also be seen in the output of fbset, which
reports "accel true".

Fixes: ee4cce0a8f03a333 ("drm/fb-helper: fix input validation gaps in check_var")
Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Tested-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
---
v2:
   - Add Reviewed-by, Tested-by.
---
  drivers/gpu/drm/drm_fb_helper.c | 12 +++++++-----
  1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index f0e9549b6bd751de..8dc376b771d2cf22 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1379,17 +1379,19 @@ static void drm_fb_helper_fill_pixel_fmt(struct fb_var_screeninfo *var,
  	}
  }
-static void __fill_var(struct fb_var_screeninfo *var,
+static void __fill_var(struct fb_var_screeninfo *var, struct fb_info *info,
  		       struct drm_framebuffer *fb)
  {
  	int i;
var->xres_virtual = fb->width;
  	var->yres_virtual = fb->height;
-	var->accel_flags = FB_ACCELF_TEXT;
+	var->accel_flags = 0;
  	var->bits_per_pixel = drm_format_info_bpp(fb->format, 0);
- var->height = var->width = 0;
+	var->height = info->var.height;
+	var->width = info->var.width;
+
  	var->left_margin = var->right_margin = 0;
  	var->upper_margin = var->lower_margin = 0;
  	var->hsync_len = var->vsync_len = 0;
@@ -1452,7 +1454,7 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
  		return -EINVAL;
  	}
- __fill_var(var, fb);
+	__fill_var(var, info, fb);
/*
  	 * fb_pan_display() validates this, but fb_set_par() doesn't and just
@@ -1908,7 +1910,7 @@ static void drm_fb_helper_fill_var(struct fb_info *info,
  	info->pseudo_palette = fb_helper->pseudo_palette;
  	info->var.xoffset = 0;
  	info->var.yoffset = 0;
-	__fill_var(&info->var, fb);
+	__fill_var(&info->var, info, fb);
  	info->var.activate = FB_ACTIVATE_NOW;
drm_fb_helper_fill_pixel_fmt(&info->var, format);

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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