Re: [RFC/PATCH] remove gratuitous reads from maple pci config space methods
From: David Gibson <hidden>
Date: 2007-08-09 03:05:55
On Wed, Aug 08, 2007 at 07:50:44PM -0500, Nathan Lynch wrote:
The maple pci configuration space write methods read 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.
It might be worth checking that there isn't a particular reason for these. Just because posting writes are forbidden doesn't mean a particular bridge won't screw it up...
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. It definitely causes a system hang for me with a Broadcom 5721 PCIE network adapter, which is fixed by this change. Remove the gratuitous reads from u3_agp_write_config, u3_ht_write_config, and u4_pcie_write_config.
-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson