[RFC] drm/fb-helper: reject any changes to the fbdev

[Tomi Valkeinen]

On 12/10/16 02:15, Stefan Agner wrote:
> The current fbdev emulation does not allow to push back changes in
> width, height or depth to KMS, hence reject any changes with an
> error. This makes sure that fbdev ioctl's fail properly and user
> space does not assume that changes succeeded.

The description is a bit confusing. Don't you mean that currently the
fbdev emulation does allow changes, but doesn't actually push those
changes to KMS? And this patch makes the driver reject those changes.

The change itself sounds good to me.

Reviewed-by: Tomi Valkeinen <tomi.valkeinen at ti.com>

> Signed-off-by: Stefan Agner <stefan at agner.ch>
> ---
> This rejects reconfiguration of framebuffer like
> fbset -rgba 5,6,5 -depth 16 (when in 24 bit mode by default)
> fbset -xres 123
> 
> I think all users of drm_fb_helper_check_var use also the generic
> drm_fb_helper_set_par (or do otherwise not support changing size/
> depth). Hence, afaict, the change should be the right thing to do
> for all driver...
> 
>  drivers/gpu/drm/drm_fb_helper.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 03414bd..596c056 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1211,11 +1211,14 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
>  	if (var->pixclock != 0 || in_dbg_master())
>  		return -EINVAL;
>  
> -	/* Need to resize the fb object !!! */
> -	if (var->bits_per_pixel > fb->bits_per_pixel ||
> -	    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 is greater than current fb "
> +	/*
> +	 * 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->bits_per_pixel ||
> +	    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,
>  			  var->xres_virtual, var->yres_virtual,
> 

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