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

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Date:   Wed, 24 May 2023 13:41:30 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Javier Martinez Canillas <javierm@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sui Jingfeng <suijingfeng@...ngson.cn>
Subject: Re: [PATCH v2] drm/fb-helper: Fix height, width, and accel_flags in
 fb_var

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@...der.be>
> Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> Tested-by: Sui Jingfeng <suijingfeng@...ngson.cn>
> ---
> 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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