[PATCH V4] PCI: handle CRS returned by device after FLR

[Sinan Kaya]

An endpoint is allowed to issue Configuration Request Retry Status (CRS)
following a Function Level Reset (FLR) request to indicate that it is not
ready to accept new requests.

Seen a timeout message with Intel 750 NVMe drive and FLR reset.

Kernel enables CRS visibility in pci_enable_crs() function for each bridge
it discovers. The OS observes a special vendor ID read value of 0xFFFF0001
in this case. We need to keep polling until this special read value
disappears. pci_bus_read_dev_vendor_id() takes care of CRS handling for a
given vendor id read request under the covers.

Adding a vendor ID read if this is a physical function before attempting
to read any other registers on the endpoint. A CRS indication will only
be given if the address to be read is vendor ID register.

Note that virtual functions report their vendor ID through another
mechanism.

The spec is calling to wait up to 1 seconds if the device is sending CRS.
The NVMe device seems to be requiring more. Relax this up to 60 seconds.

Signed-off-by: Sinan Kaya <okaya at codeaurora.org>
---
 drivers/pci/pci.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index aab9d51..83a9784 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3723,10 +3723,16 @@ static void pci_flr_wait(struct pci_dev *dev)
 	int i = 0;
 	u32 id;
 
-	do {
-		msleep(100);
-		pci_read_config_dword(dev, PCI_COMMAND, &id);
-	} while (i++ < 10 && id == ~0);
+	if (dev->is_virtfn) {
+		do {
+			msleep(100);
+			pci_read_config_dword(dev, PCI_COMMAND, &id);
+		} while (i++ < 10 && id == ~0);
+	} else {
+		if (!pci_bus_read_dev_vendor_id(dev->bus, dev->devfn, &id,
+						60*1000))
+			id = ~0;
+	}
 
 	if (id == ~0)
 		dev_warn(&dev->dev, "Failed to return from FLR\n");
-- 
1.9.1