On Mon, Jun 12, 2017 at 2:48 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > On Fri, Jun 09, 2017 at 04:16:17PM -0700, Yinghai Lu wrote: >> From: James Puthukattukaran <james.puthukattukaran@xxxxxxxxxx> >> >> The IDT switch incorrectly flags an ACS source violation on a read config >> request to an end point device on the completion (IDT 89H32H8G3-YC, >> errata #36) even though the PCI Express spec states that completions are >> never affected by ACS source violation (PCI Spec 3.1, Section 6.12.1.1). > > Can you include a URL where this erratum is published? If not, can > you include the actual erratum text here? Ok. > > Have you considered ways to make this patch apply only to the affected > IDT switches? Currently it applies to *all* devices. But we need to apply that workaround before we know vendorid/deviceid under that root port or downstream port. > > The purpose of the pci_bus_read_dev_vendor_id() path is to support the > Configuration Request Retry Status feature (see PCIe r3.1, sec 2.3.2), > which works by special handling of config reads of the Vendor ID after > a reset. Normally, that Vendor ID read would be the first access to > a device when we enumerate it. > > This patch adds config reads and writes of the ACS capability *before* > the Vendor ID read. At that point we don't even know whether the > device exists. If it doesn't exist, pci_find_ext_capability() would > read 0xffffffff data, and it probably fails reasonably gracefully. > > But if the device *does* exist, I think this patch breaks the CRS > Software Visibility feature. Without this patch, we try to read > Vendor ID, and the device may return a CRS Completion Status. If CRS > visibility is enabled, the root complex may complete the request by > returning 0x0001 for the Vendor ID, in which case we sleep and try > again later. > > With this patch, we first try to read the ACS capability. If the > device returns a CRS Completion Status, the root complex is required > to reissue the config request. This is the required behavior > regardless of whether CRS Software Visibility is enabled, so I think > this effectively disables that feature. The workaround (acs reading etc) is applied to root port or downstream port. and pci_bus_read_dev_vendor_id() is for reading vendorid of device under that root port or downstream port. Thanks Yinghai
