[Dri-devel] radeon dri + software suspend/resume

[Charl P. B. <c.p...@it...>]

Dear list,

Now I am trying to get software suspend going with DRI Radeon; this is also
the reason why I wanted to get the VT switch fixed first.

In anycase, swsusp is a patch that allows a running linux machine to be
suspended to disc without assistance from the hardware.  This is often used
on more modern laptops with only ACPI support (i.e. no APM).  According to
the ACPI standard, the OS is responsible for much of the effort of saving
state to disc and restoring again during an S4 sleep state.

swsusp, although often used together with ACPI, is not a real S4 yet, but
functionally it's the same.  However, device drivers are responsible for
making sure that the hardware state that they control is the same before and
after the state.

So, swsusp works fine without agpgart and dri.  I can suspend and resume to
my heart's content.  However, with agpgart and dri this does NOT work.  The
machine resumes into a garbled X display.  X is at 100% but the machine is
reachable by network.  Sound familiar? ;)

I've already hacked agpgart so that its resume function does something
sensible with the hardware.  I've also kludged the RADEONEnterVT() function
in radeon_driver.c so that it re-calls drmEnable() and of course activates
the bus mastering. The PCI config of the Radeon device is identical before
and after a suspend/resume except for Master-Abort which is active after the
resume.  My naive theory is that the host is trying to speak to the Radeon
but the Radeon, having just booted, doesn't know about anything.

My next step is to start hacking at the radeon drm driver, as I believe that
one should be able to store hardware state in memory and restore it after
resuming.  My first target is of course reloading the command processor
microcode.

Now the actual question: Besides the microcode, what other Radeon hardware
state gets lost across a machine reboot?  I.e. what is the minimum that I
have to store before we go down for a suspend?

I believe that the driver api allows for suspend and resume hooks to be
supplied.  I am planning to take this route.

Thanks for ANY advice.

Best regards,
Charl

-- 
charl p. botha http://cpbotha.net/ http://visualisation.tudelft.nl/