int xxxfb_check_var (struct fb_var_screeninfo * var, struct fb_info * info);
Checks to see if the hardware supports the state requested by var passed in. This function does not alter the hardware state!!! This means the data stored in struct fb_info and struct xxx_par do not change. This includes the var inside of struct fb_info. Do NOT change these. This function can be called on its own if we intent to only test a mode and not actually set it. The stuff in modedb.c is a example of this. If the var passed in is slightly off by what the hardware can support then we alter the var PASSED in to what we can do. If the hardware doesn't support mode change a -EINVAL will be returned by the upper layers. You don't need to implement this function then. If you hardware doesn't support changing the resolution then this function is not needed. In this case the driver woudl just provide a var that represents the static state the screen is in.
Returns negative errno on error, or zero on success.