Re: [PATCH v2] drm: fb-helper: Reject all pixel format changing requests

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Oct 03, 2018 at 07:45:38PM +0300, Eugeniy Paltsev wrote:
> drm fbdev emulation doesn't support changing the pixel format at all,
> so reject all pixel format changing requests.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
> ---
> Changes v1->v2:
>  * Reject all pixel format changing request, not just the invalid ones.
> 
>  drivers/gpu/drm/drm_fb_helper.c | 91 ++++++++++++-----------------------------
>  1 file changed, 26 insertions(+), 65 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 16ec93b75dbf..48598d7f673f 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1580,6 +1580,25 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
>  }
>  EXPORT_SYMBOL(drm_fb_helper_ioctl);
>  
> +static bool drm_fb_pixel_format_equal(const struct fb_var_screeninfo *var_1,
> +				      const struct fb_var_screeninfo *var_2)
> +{
> +	return var_1->bits_per_pixel == var_2->bits_per_pixel &&
> +	       var_1->grayscale == var_2->grayscale &&
> +	       var_1->red.offset == var_2->red.offset &&
> +	       var_1->red.length == var_2->red.length &&
> +	       var_1->red.msb_right == var_2->red.msb_right &&
> +	       var_1->green.offset == var_2->green.offset &&
> +	       var_1->green.length == var_2->green.length &&
> +	       var_1->green.msb_right == var_2->green.msb_right &&
> +	       var_1->blue.offset == var_2->blue.offset &&
> +	       var_1->blue.length == var_2->blue.length &&
> +	       var_1->blue.msb_right == var_2->blue.msb_right &&
> +	       var_1->transp.offset == var_2->transp.offset &&
> +	       var_1->transp.length == var_2->transp.length &&
> +	       var_1->transp.msb_right == var_2->transp.msb_right;
> +}

Could have shortened a bit with memcmp() but this works too.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

I suppose we really should be doing the same for most of the rest of
var_screeninfo as we don't allow changing the timings/etc. either.

> +
>  /**
>   * drm_fb_helper_check_var - implementation for &fb_ops.fb_check_var
>   * @var: screeninfo to check
> @@ -1590,7 +1609,6 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
>  {
>  	struct drm_fb_helper *fb_helper = info->par;
>  	struct drm_framebuffer *fb = fb_helper->fb;
> -	int depth;
>  
>  	if (var->pixclock != 0 || in_dbg_master())
>  		return -EINVAL;
> @@ -1610,72 +1628,15 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
>  		return -EINVAL;
>  	}
>  
> -	switch (var->bits_per_pixel) {
> -	case 16:
> -		depth = (var->green.length == 6) ? 16 : 15;
> -		break;
> -	case 32:
> -		depth = (var->transp.length > 0) ? 32 : 24;
> -		break;
> -	default:
> -		depth = var->bits_per_pixel;
> -		break;
> -	}
> -
> -	switch (depth) {
> -	case 8:
> -		var->red.offset = 0;
> -		var->green.offset = 0;
> -		var->blue.offset = 0;
> -		var->red.length = 8;
> -		var->green.length = 8;
> -		var->blue.length = 8;
> -		var->transp.length = 0;
> -		var->transp.offset = 0;
> -		break;
> -	case 15:
> -		var->red.offset = 10;
> -		var->green.offset = 5;
> -		var->blue.offset = 0;
> -		var->red.length = 5;
> -		var->green.length = 5;
> -		var->blue.length = 5;
> -		var->transp.length = 1;
> -		var->transp.offset = 15;
> -		break;
> -	case 16:
> -		var->red.offset = 11;
> -		var->green.offset = 5;
> -		var->blue.offset = 0;
> -		var->red.length = 5;
> -		var->green.length = 6;
> -		var->blue.length = 5;
> -		var->transp.length = 0;
> -		var->transp.offset = 0;
> -		break;
> -	case 24:
> -		var->red.offset = 16;
> -		var->green.offset = 8;
> -		var->blue.offset = 0;
> -		var->red.length = 8;
> -		var->green.length = 8;
> -		var->blue.length = 8;
> -		var->transp.length = 0;
> -		var->transp.offset = 0;
> -		break;
> -	case 32:
> -		var->red.offset = 16;
> -		var->green.offset = 8;
> -		var->blue.offset = 0;
> -		var->red.length = 8;
> -		var->green.length = 8;
> -		var->blue.length = 8;
> -		var->transp.length = 8;
> -		var->transp.offset = 24;
> -		break;
> -	default:
> +	/*
> +	 * drm fbdev emulation doesn't support changing the pixel format at all,
> +	 * so reject all pixel format changing requests.
> +	 */
> +	if (!drm_fb_pixel_format_equal(var, &info->var)) {
> +		DRM_DEBUG("fbdev emulation doesn't support changing the pixel format\n");
>  		return -EINVAL;
>  	}
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_fb_helper_check_var);
> -- 
> 2.14.4
> 
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-- 
Ville Syrjälä
Intel