Re: [ACPI] [Proposal]Another way to save/restore PCI config space for suspend/resume

[Andi Kleen]

On Tue, Oct 26, 2004 at 12:50:57PM +0800, Li Shaohua wrote:
> Hi,
> We suffer from PCI config space issue for a long time, which causes many
> system can't correctly resume. Current Linux mechanism isn't sufficient.
> Here is a another idea: 
> Record all PCI writes in Linux kernel, and redo all the write after
> resume in order. The idea assumes Firmware will restore all PCI config

This won't work very well for some cases. e.g. on AMD x86-64 the 
IOMMU is flushed by setting/clearing a bit in PCI config space.
AGP implementations work similar. You really don't want to track
all these flushes, it would be far too costly.

> space to the boot time state, which is true at least for IA32.
> 
> Reason:
> 1. Current PCI save/restore routines only cover first 64 bytes

The driver could set a flag if it wants more.

> 2. No PCI bridge driver currently.

That could be fixed I guess? 

> 3. Some special devices can't or are difficult to save/restore config
> space with current model. Such as PCI link device, it's a sysdev, but
> its resume code can't be invoked with irq disabled.

In this case it would be IMHO better to have specialized suspend/resume
functions in the drivers for these oddball devices.

Most likely they will require some special handling anyways
(like special delays etc.) that can't be done by the generic code 

> 4. ACPI possibly changes special devices' config space, such as host
> bridge or LPC bridge. The special devices generally are vender specific,
> and possibly will not have a driver forever.

I didn't get that one.

-Andi
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