Re: Subtle semantic issue with sleep callbacks in drivers

[Jeff Garzik <jgarzik@pobox.com>]

On Thu, Apr 17, 2003 at 02:35:50PM +0100, Alan Cox wrote:
> On Mer, 2003-04-16 at 19:39, Patrick Mochel wrote:
> > I completely agree with Andy. We should not re-POST the video hardware, no
> > matter what. The idea behind ACPI is that the OS takes care of everything, 
> > including video save/restore. 
> 
> Outside of happyville ivory towers you probably have no choice. Only the
> BIOS knows stuff like the RAM timings, and some windows drivers just use
> the BIOS, others rely on being shipped compiled for the right variant of
> card they came with.

You are exactly right.

The video BIOS on a card often contains information that is found
-nowhere- else.  Not in the chip docs.  Not in a device driver.
Such information can and does vary from board-to-board, such as RAM
timings, while the chip remains unchanged.

You mention "windows drivers" above... even some Linux X drivers
depend on video BIOS.  The S3 Savage XFree86 driver, for example,
uses video BIOS quite heavily unless you tell it not to (or are on
a platform that prevents such).

WRT save and restore, it is certainly possible without video re-POST...

However, support such will require a monumental effort of testing and
debugging for each video board.  This monumental effort _will_ include
XFree86 hacking and possibly the additional of some save-n-restore
video drivers, if we do not wish to simply require CONFIG_FBDEV if
CONFIG_SUSPEND is set.

Video re-POST is simply a Real Life(tm) shortcut to that monumental effort.

	Jeff, originally an fbdev hacker back in the day...