[PATCH 1/2] PCI: Don't treat ~0 as ready in pci_dev_wait() with RRS SV

[Alexander Gruhlke <gruhlke@mailbox.org>]

With RRS Software Visibility, pci_dev_wait() considers a device ready as
soon as reading the Vendor ID doesn't return the RRS value.  Some devices
don't respond with RRS while they aren't ready, so the read returns ~0
and pci_dev_wait() stops waiting too early.  This was seen with Intel
[8086:0a54] and Samsung [144d:a80c] NVMe SSDs.

Also check the Command register for ~0, as without RRS Software
Visibility.

Fixes: d591f6804e7e ("PCI: Wait for device readiness with Configuration RRS")
Link: https://lore.kernel.org/r/20250611101442.387378-1-hui.wang@canonical.com
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Alexander Gruhlke <gruhlke@mailbox.org>
---
 drivers/pci/pci.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 350bae907e..26be5d1ca9 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1215,7 +1215,8 @@ static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
 	 * If the device is below a Root Port with Configuration RRS
 	 * Software Visibility enabled, reading the Vendor ID returns a
 	 * special data value if the device responded with RRS.  Read the
-	 * Vendor ID until we get non-RRS status.
+	 * Vendor ID until we get non-RRS status, then the Command register
+	 * as below.
 	 *
 	 * If there's no Root Port or Configuration RRS Software Visibility
 	 * is not enabled, the device may still respond with RRS, but
@@ -1235,8 +1236,11 @@ static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
 
 		if (root && root->config_rrs_sv) {
 			pci_read_config_dword(dev, PCI_VENDOR_ID, &id);
-			if (!pci_bus_rrs_vendor_id(id))
-				break;
+			if (!pci_bus_rrs_vendor_id(id)) {
+				pci_read_config_dword(dev, PCI_COMMAND, &id);
+				if (!PCI_POSSIBLE_ERROR(id))
+					break;
+			}
 		} else {
 			pci_read_config_dword(dev, PCI_COMMAND, &id);
 			if (!PCI_POSSIBLE_ERROR(id))
-- 
2.56.0