Improve PCI config space writeback.

Improve PCI config space writeback.

[Dave Jones]

At least one laptop blew up on resume from suspend with a black screen
due to a lack of this patch.  By only writing back config space that
is different, we minimise the possibility of accidents like this.

Signed-off-by: Dave Jones <davej@redhat.com>


--- linux-2.6.16.noarch/drivers/pci/pci.c~	2006-04-16 17:36:34.000000000 -0500
+++ linux-2.6.16.noarch/drivers/pci/pci.c	2006-04-16 17:37:42.000000000 -0500
@@ -461,9 +461,17 @@ int 
 pci_restore_state(struct pci_dev *dev)
 {
 	int i;
+	int val;
 
-	for (i = 0; i < 16; i++)
-		pci_write_config_dword(dev,i * 4, dev->saved_config_space[i]);
+	for (i = 0; i < 16; i++) {
+		pci_read_config_dword(dev, i * 4, &val);
+		if (val != dev->saved_config_space[i]) {
+			printk (KERN_DEBUG "PM: Writing back config space on device %s at offset %x. (Was %x, writing %x)\n",
+				pci_name(dev), i,
+				val, (int) dev->saved_config_space[i]);
+			pci_write_config_dword(dev,i * 4, dev->saved_config_space[i]);
+		}
+	}
 	pci_restore_msi_state(dev);
 	pci_restore_msix_state(dev);
 	return 0;

Re: Improve PCI config space writeback.

[Benjamin Herrenschmidt]

On Sun, 2006-04-16 at 17:42 -0500, Dave Jones wrote:
> At least one laptop blew up on resume from suspend with a black screen
> due to a lack of this patch.  By only writing back config space that
> is different, we minimise the possibility of accidents like this.
> 
> Signed-off-by: Dave Jones <davej@redhat.com>

I think it's a mistake to restore the command register before the rest.
It should be restored last.

> 
> --- linux-2.6.16.noarch/drivers/pci/pci.c~	2006-04-16 17:36:34.000000000 -0500
> +++ linux-2.6.16.noarch/drivers/pci/pci.c	2006-04-16 17:37:42.000000000 -0500
> @@ -461,9 +461,17 @@ int 
>  pci_restore_state(struct pci_dev *dev)
>  {
>  	int i;
> +	int val;
>  
> -	for (i = 0; i < 16; i++)
> -		pci_write_config_dword(dev,i * 4, dev->saved_config_space[i]);
> +	for (i = 0; i < 16; i++) {
> +		pci_read_config_dword(dev, i * 4, &val);
> +		if (val != dev->saved_config_space[i]) {
> +			printk (KERN_DEBUG "PM: Writing back config space on device %s at offset %x. (Was %x, writing %x)\n",
> +				pci_name(dev), i,
> +				val, (int) dev->saved_config_space[i]);
> +			pci_write_config_dword(dev,i * 4, dev->saved_config_space[i]);
> +		}
> +	}
>  	pci_restore_msi_state(dev);
>  	pci_restore_msix_state(dev);
>  	return 0;
> -
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Re: Improve PCI config space writeback.

[Dave Jones]

On Mon, Apr 17, 2006 at 10:27:07AM +1000, Ben Herrenschmidt wrote:
 > On Sun, 2006-04-16 at 17:42 -0500, Dave Jones wrote:
 > > At least one laptop blew up on resume from suspend with a black screen
 > > due to a lack of this patch.  By only writing back config space that
 > > is different, we minimise the possibility of accidents like this.
 > > 
 > > Signed-off-by: Dave Jones <davej@redhat.com>
 > 
 > I think it's a mistake to restore the command register before the rest.
 > It should be restored last.

Adam Belay had a patch that did this, and a bunch of other similar
things (like making sure we never set BIST when restoring).

There are likely a number of similar possible improvements.

		Dave

-- 
http://www.codemonkey.org.uk