On Tue, 2011-09-27 at 10:07 -0500, Jon Mason wrote:
> On Sun, Sep 25, 2011 at 11:56 PM, Benjamin Herrenschmidt
> <benh@xxxxxxxxxxxxxxxxxxx> wrote:
> > When configuring the PCIe settings for "performance", we allow parents
> > to have a larger Max Payload Size than children and rely on children
> > Max Read Request Size to not be larger than their own MPS to avoid
> > having the host bridge generate responses they can't cope with.
> >
> > However, various drivers in Linux call pci_set_readrq() with arbitrary
> > values, assuming this to be a simple performance tweak. This breaks
> > under our "performance" configuration.
> >
> > Fix that by making sure the value programmed by pcie_set_readrq() is
> > never larger than the configured MPS for that device.
>
>
> We probably want to include this in 3.1-rcX as well. I can ack this
> one and send it with my other patch (assuming no issues are found).
> Let me know.
Sure.
Cheers,
Ben.
> Thanks,
> Jon
>
> >
> > Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > ---
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 4e84fd4..d369316 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -3203,8 +3203,6 @@ int pcie_set_readrq(struct pci_dev *dev, int rq)
> > if (rq < 128 || rq > 4096 || !is_power_of_2(rq))
> > goto out;
> >
> > - v = (ffs(rq) - 8) << 12;
> > -
> > cap = pci_pcie_cap(dev);
> > if (!cap)
> > goto out;
> > @@ -3212,6 +3210,22 @@ int pcie_set_readrq(struct pci_dev *dev, int rq)
> > err = pci_read_config_word(dev, cap + PCI_EXP_DEVCTL, &ctl);
> > if (err)
> > goto out;
> > + /*
> > + * If using the "performance" PCIe config, we clamp the
> > + * read rq size to the max packet size to prevent the
> > + * host bridge generating requests larger than we can
> > + * cope with
> > + */
> > + if (pcie_bus_config == PCIE_BUS_PERFORMANCE) {
> > + int mps = pcie_get_mps(dev);
> > +
> > + if (mps < 0)
> > + return mps;
> > + if (mps < rq)
> > + rq = mps;
> > + }
> > +
> > + v = (ffs(rq) - 8) << 12;
> >
> > if ((ctl & PCI_EXP_DEVCTL_READRQ) != v) {
> > ctl &= ~PCI_EXP_DEVCTL_READRQ;
> >
> >
> > --
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