On Thu, 07 Mar 2019, Tom Li <tomli@xxxxxxxx> wrote: > Hi all. > > As you may have noticed, recently I've been working on a reworked version > of sm712fb, and planned to convert it to a DRM/KMS driver. Besides using > it on embedded/non-x86 systems, I thought it would be a good idea to support > histrocial x86 laptops with this VGA chipset as well, so I've acquired a > machine for testing. > > However, soon I found a nasty problem. The BIOS does not reset the chip > on boot! Like most graphics controller of that era, sm712 chipset has a > VGA compatible mode and a 2D framebuffer mode. The power-on default is > VGA. The BIOS writer just assumed this, and does nothing to reinitialize > it. If one uses the framebuffer driver under Linux, once the machine reboots, > the entire LCD panel becomes a piece of garbage. > > AFAIK, the framebuffer driver would be running throughout the kernel's life- > cycle, is it really possible to workaround this issue by restoring on VGA > state upon reboot? It's possible to do this using a reboot notifier. I am not sure if there are better ways to achieve the same, but there's at least one example of using reboot notifiers to achieve the exact same goal. See drivers/video/fbdev/aty/atyfb_base.c, look for register_reboot_notifier(). HTH, Jani. -- Jani Nikula, Intel Open Source Graphics Center
