Subject: Re: [RFC/PATCH] remove gratuitous reads from maple pci config space methods

From: Benjamin Herrenschmidt <[email-masked]>
Date: Thu, 09 Aug 2007 10:55:33 +1000

On Wed, 2007-08-08 at 19:50 -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.  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.
> 
> Signed-off-by: Nathan Lynch <[email-masked]>

Acked-by: Benjamin Herrenschmidt <[email-masked]>
---

Thanks ! Care to fix powermac too ? :-)

Cheers,
Ben.

> ---
>  arch/powerpc/platforms/maple/pci.c |    9 ---------
>  1 files changed, 0 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/maple/pci.c b/arch/powerpc/platforms/maple/pci.c
> index 2542403..b095eaa 100644
> --- a/arch/powerpc/platforms/maple/pci.c
> +++ b/arch/powerpc/platforms/maple/pci.c
> @@ -169,15 +169,12 @@ static int u3_agp_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;
> @@ -268,15 +265,12 @@ static int u3_ht_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;
> @@ -376,15 +370,12 @@ static int u4_pcie_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;