[Linux-fbdev-devel] Comments on fbgen.c and fbcon-accel.c

[Antonino D. <ad...@po...>]

Hi,

I have a few observations on fbgen and fbcon-accel.

1.  fbcon_accel_clear_margins may not work correctly with fbgen since
fbcon_accel will use the xoffset and yoffset values from info->var.  

    void fbcon_accel_clear_margins(struct vc_data *vc, struct display
    *p,
    			       int bottom_only)
    {
    	<<<snip>>> 
    
    	if (bh) {
    		region.dx = info->var.xoffset;
                    region.dy = info->var.yoffset + bs;
                    region.width  = rs;
                    region.height = bh;
    		info->fbops->fb_fillrect(info, &region);
    	}
    }

However fbgen_pan_display updates the xoffset and yoffset in
fb_display[con].var. So margins don't get cleared if the driver supports
y-panning or y-wrapping.

    int fbgen_pan_display(struct fb_var_screeninfo *var, int con,
    		      struct fb_info *info)
    {
    	<<< snip >>>
    
        if (con == info->currcon) {
    	if (fbhw->pan_display) {
    	    if ((err = fbhw->pan_display(var, info2)))
    		return err;
    	} else
    	    return -EINVAL;
        }
        fb_display[con].var.xoffset = var->xoffset;
        fb_display[con].var.yoffset = var->yoffset;
    
    	<<< snip >>>
    }

2. Also, fbgen_switch basically just do an fbgen_do_set_var()
(decode_var(), followed by set_par()).  This is okay most times, but
it's probably better if fbgen_switch also does an encode_fix() since
fbcon's drawing functions also rely on fix->line_length.

If an fb_fix_screeninfo is not updated, display corruption occurs when
switching to another display with a different pixelformat.

Tony