[PATCH] remove gratuitous reads from pasemi pci config space methods

[PATCH] remove gratuitous reads from pasemi pci config space methods

[Nathan Lynch]

The pasemi pci configuration space write method reads the written
location immediately after the write is performed, presumably in order
to flush the write.  However, configuration space writes are not
allowed to be posted, making these reads gratuitous.  Furthermore,
this behavior potentially causes us to violate the PCI PM spec when
changing between e.g. D0 and D3 states, because a delay of up to 10ms
may be required before the OS accesses configuration space after the
write which initiates the transition.

Remove the unnecessary reads from pa_pxp_write_config.

Signed-off-by: Nathan Lynch <ntl@pobox.com>
---
 arch/powerpc/platforms/pasemi/pci.c |    3 ---
 1 files changed, 0 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/platforms/pasemi/pci.c b/arch/powerpc/platforms/pasemi/pci.c
index ab1f5f6..f7da373 100644
--- a/arch/powerpc/platforms/pasemi/pci.c
+++ b/arch/powerpc/platforms/pasemi/pci.c
@@ -107,15 +107,12 @@ static int pa_pxp_write_config(struct pci_bus *bus, unsigned int devfn,
 	switch (len) {
 	case 1:
 		out_8(addr, val);
-		(void) in_8(addr);
 		break;
 	case 2:
 		out_le16(addr, val);
-		(void) in_le16(addr);
 		break;
 	default:
 		out_le32(addr, val);
-		(void) in_le32(addr);
 		break;
 	}
 	return PCIBIOS_SUCCESSFUL;
-- 
1.5.2.4

Re: [PATCH] remove gratuitous reads from pasemi pci config space methods

[Olof Johansson]

On Thu, Aug 09, 2007 at 04:37:27PM -0500, Nathan Lynch wrote:
> The pasemi pci configuration space write method reads the written
> location immediately after the write is performed, presumably in order
> to flush the write.  However, configuration space writes are not
> allowed to be posted, making these reads gratuitous.  Furthermore,
> this behavior potentially causes us to violate the PCI PM spec when
> changing between e.g. D0 and D3 states, because a delay of up to 10ms
> may be required before the OS accesses configuration space after the
> write which initiates the transition.
> 
> Remove the unnecessary reads from pa_pxp_write_config.

Thanks!

> Signed-off-by: Nathan Lynch <ntl@pobox.com>

Acked-by: Olof Johansson <olof@lixom.net>


-Olof