[PATCH v9 2/4] PCI: Disable PCIe Relaxed Ordering if unsupported

Ding Tianhong
2017-08-09T13:42:48Z

On 2017/8/9 11:25, Bjorn Helgaas wrote:
> On Tue, Aug 08, 2017 at 09:22:39PM -0500, Bjorn Helgaas wrote:
>> On Sat, Aug 05, 2017 at 03:15:11PM +0800, Ding Tianhong wrote:
>>> When bit4 is set in the PCIe Device Control register, it indicates

> After looking at the driver, I wonder if it would be simpler like
> this:
>
> int pcie_relaxed_ordering_enabled(struct pci_dev *dev)
> {
> u16 ctl;
>
> pcie_capability_read_word(dev, PCI_EXP_DEVCTL, &ctl);
> return ctl & PCI_EXP_DEVCTL_RELAX_EN;
> }
> EXPORT_SYMBOL(pcie_relaxed_ordering_enabled);
>
> static void pci_configure_relaxed_ordering(struct pci_dev *dev)
> {
> struct pci_dev *root;
>
> if (dev->is_virtfn)
> return; /* PCI_EXP_DEVCTL_RELAX_EN is RsvdP in VFs */
>
> if (!pcie_relaxed_ordering_enabled(dev))
> return;
>
> /*
> * For now, we only deal with Relaxed Ordering issues with Root
> * Ports. Peer-to-peer DMA is another can of worms.
> */
> root = pci_find_pcie_root_port(dev);
> if (!root)
> return;
>
> if (root->relaxed_ordering_broken)
> pcie_capability_clear_word(dev, PCI_EXP_DEVCTL,
> PCI_EXP_DEVCTL_RELAX_EN);
> }
>
> This doesn't check every intervening switch, but I don't think we know
> about any issues except with root ports.
>

Yes

> And the driver could do:
>
> if (!pcie_relaxed_ordering_enabled(pdev))
> adapter->flags |= ROOT_NO_RELAXED_ORDERING;
>
> The driver code wouldn't show anything about coherent memory vs.
> peer-to-peer, but we really don't have a clue about how to handle that
> yet anyway.
>
> I guess this is back to exactly what you proposed, except that I
> changed the name of pcie_relaxed_ordering_supported() to
> pcie_relaxed_ordering_enabled(), which I think is slightly more
> specific from the device's point of view.
>

OK, looks like we reach a consensus finally, I will follow your new opinion and resend, thanks.

Ding

> Bjorn
>
> .
>