Re: [RFC] Reliable video POSTing on resume (was: Re: [ACPI] Samsung P35, S3, black screen (radeon))

[ebiederm@xmission.com (Eric W. Biederman)]

Pavel Machek <pavel@ucw.cz> writes:

> Hi!
> 
> > > We already try to do that, but it hangs on 70% of machines. See
> > > Documentation/power/video.txt.
> > 
> > We know that all of these ROMs are run at power on so they have to
> > work. This implies that there must be something wrong with the
> > environment the ROM are being run in. Video ROMs make calls into the
> > INT vectors of the system BIOS. If these haven't been set up yet
> > running the VBIOS is sure to hang.  Has someone with ROM source and
> > the appropriate debugging tools tried to debug one of these hangs?
> > Alternatively code could be added to wakeup.S to try and set these up
> > or dump the ones that are there and see if they are sane.
> 
> Rumors say that notebooks no longer have video bios at C000h:0; rumors
> say that video BIOS on notebooks is simply integrated into main system
> BIOS. I personaly do not know if rumors are true, but PCs are ugly
> machines....

The state of current hardware has already been mentioned but let
me clarify.  This is not a laptop problem anytime you have onboard
video you are unlikely to have a separate video ROM.  This includes
many recent server boards as well as laptops.  When the board boots
up there will be a video option ROM shadowed into the usually location
at C000h:0 but what becomes of it afterwards is a good question.

For server boards most commonly this seems to be a flavor of the ATI
Rage XL chip.  It is a low end part that I doubt getting documentation
for will be very hard.   And according to
Documentation/power/video.txt this is one of the cases that actually
works.

What is happening in those POST routines of a video card is typically
the code to initialize the memory controller on the video card.  Plus
a little bit of code to set the video mode.  If I read the
documentation correctly in a S3 power state only the RAM is preserved.
So it does look like the video post is needed.

Hmm.  Looking at the ACPI 3.0 spec it appears there is a _ROM method
that can be called to get a copy of the ROM image for an onboard
video card.  Has any one tried that method?

Eric