[ltp] Re: ACPI S3 works fine on T41p (Was: ACPI sleep works first time)

[Alexander Gran]

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Am Donnerstag, 26. August 2004 00:26 schrieb Volker Braun:
> Since you are the radeon specialist :-), what is your opinion on the
> "radeonfb: suspending to state: 2" (acpi) vs. "state: 3" (apm)
> as mentioned in the kernel bugzilla. Does this for sure not make any
> difference?

Ahh,yes. I just send an other info asking for that. Well this is the problem:
First of all, we have quite some confusion in the kernel regarding translation 
between PCI, ACPI System, ACPI PCI, Apm power states. All these are plain 
ints and are passed around without conversion. In this case it's basically 
the follwoing problem:
You ask for S3. This is an int 3. If This translated to PCI state 3, 
everything would be fine (The case when using APM). However the dsdt returns 
(I dont yet know in which S?? method, so I cannot fix it yet) a 2. The 
kernel, doing no conversion or something passes this as a PCI state to the 
devices. However, PCI state 2 is
1. Not supported by all devices. This is the reason some people get these 
"Could not suspend device" messages.
2. It does not save as much power as PCI state 3 (I save you from the details 
here). Even if your system enters this ACPI S3, PCI state 2 mode, it will eat 
up more power.
You can try to fix that by patching drivers/base/power/suspend.c. Just insert 

if(state == 2)
 state =3;

after

int device_suspend(u32 state)
{
        int error = 0;

This could save some more power. However the acpi stuff is not always able to 
get the system back on. 
Next point: Not all devices are suspended (e.g. Ultrabay LED stays lid). 
Windows does this. If I understand the ACPI specs right, this is also an dsdt 
issue. No idea how to fix this..

regards
Alex



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