[PATCH] ssb: Clear RETRY_TIMEOUT in PCI Configuration

[John W. Linville]

On Wed, Nov 10, 2010 at 12:13:35AM +0100, Michael Büsch wrote:
> On Wed, 2010-11-10 at 00:09 +0100, Rafał Miłecki wrote: 
> > 2010/10/19 Michael Büsch <mb at bu3sch.de>:
> > > On Tue, 2010-10-19 at 12:55 -0500, Larry Finger wrote:
> > >> MMIO log traces obtained using the Broadcom wl hybrid driver show that
> > >> the RETRY_TIMEOUT register (0x41) in PCI configuration space is cleared
> > >> if non-zero. Similar code found in other drivers such as ipw2100 show
> > >> this operation is needed to keep PCI Tx retries from interfering with
> > >> C3 CPU state. There are no known cases where omission of this code has
> > >> caused a problem, but this patch is offered just in case such a situation
> > >> occurs.
> > >>
> > >> Signed-off-by: Larry Finger <Larry.Finger at lwfinger.net>
> > >> ---
> > >>
> > >> John,
> > >>
> > >> No particular urgency for this patch.
> > >>
> > >> Larry
> > >> ---
> > >>
> > >> Index: wireless-testing/drivers/ssb/driver_pcicore.c
> > >> ===================================================================
> > >> --- wireless-testing.orig/drivers/ssb/driver_pcicore.c
> > >> +++ wireless-testing/drivers/ssb/driver_pcicore.c
> > >> @@ -271,6 +271,7 @@ int ssb_pcicore_plat_dev_init(struct pci
> > >>  static void ssb_pcicore_fixup_pcibridge(struct pci_dev *dev)
> > >>  {
> > >>       u8 lat;
> > >> +     u32 val;
> > >>
> > >>       if (dev->bus->ops != &ssb_pcicore_pciops) {
> > >>               /* This is not a device on the PCI-core bridge. */
> > >> @@ -288,6 +289,12 @@ static void ssb_pcicore_fixup_pcibridge(
> > >>               return;
> > >>       }
> > >>
> > >> +     /* Disable the RETRY_TIMEOUT register (0x41) to keep
> > >> +      * PCI Tx retries from interfering with C3 CPU state */
> > >> +     pci_read_config_dword(pci_dev, 0x40, &val);
> > >> +     if ((val & 0x0000ff00) != 0)
> > >> +             pci_write_config_dword(pci_dev, 0x40, val & 0xffff00ff);
> > >> +
> > >>       /* Enable PCI bridge BAR1 prefetch and burst */
> > >>       pci_write_config_dword(dev, SSB_BAR1_CONTROL, 3);
> > >
> > >
> > > Hm, do you realize that this function will only be executed for PCI
> > > devices that live on top of a native SSB bus? Is that intentional?
> > >
> > > It won't affect normal broadcom wireless PCI devices.
> > > It will only have an affect on a broadcom wireless PCI device that lives
> > > behind a SSB->PCI bridge on an embedded device.
> > 
> > Is this patch needed? Shouldn't this be replaced by second version
> > affecting "normal devices"?
> > 
> > I can see both applied to wireless-testing.
> 
> They certainly should _not_ be applied both.
> John, some fixing is needed. Please remove this patch.

Does the other patch handle this case (i.e. devices behind SSB->PCI
bridge)?  If so, can you explain how?  It looks to me like the code
in ssb_pcihost_register is only called for PCI-attached b43 (or b44)
devices.

Or are you saying the RETRY_TIMEOUT change is inappropriate for a
device behind an SSB->PCI bridge?

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville at tuxdriver.com			might be all we have.  Be ready.