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

[Daniel Vetter]

On Wed, Oct 12, 2016 at 12:37:07PM +0300, Tomi Valkeinen wrote:
> 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>

Applied to drm-misc, thanks.
-Daniel

> 
> > 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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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch