Re: [Linux-fbdev-devel] Supporting various depth

[James S. <jsi...@tr...>]

> > int fb_set_var(struct fb_var_screeninfo *var, struct fb_info *info)
> > {
> >     int oldbpp, err;
> > 
> >     if (memcmp(&info->var, var, sizeof(var))) {
> >         if ((err = info->fbops->fb_check_var(var, info)))
> >                 return err;
> 
> This is not correct, since it first overwrites the old var, then checks whether
> the new one is valid. If that test fails, you're left with an invalid var in
> info->var.

That is a memory compare. It checks to see if the purposed mode is the
same as the current mode. If not then fb_check_var is called to test the
new var. info->var = var only if var->activate == FB_ACTIVATE_NOW and
their is a set_par function. You can set info->var = *var before set_par
is called because we trust check_var did its job.