Re: [PATCH v2 1/4] PCI: Check PCI_PM_CTRL in pci_dev_wait()

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On 7/11/2024 10:07, Ilpo Järvinen wrote:
On Wed, 10 Jul 2024, superm1@xxxxxxxxxx wrote:

From: Mario Limonciello <mario.limonciello@xxxxxxx>

A device that has gone through a reset may return a value in PCI_COMMAND
but that doesn't mean it's finished transitioning to D0.  On devices that
support power management explicitly check PCI_PM_CTRL on everything but
system resume to ensure the transition happened.

Devices that don't support power management and system resume will
continue to use PCI_COMMAND.

Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
  drivers/pci/pci.c | 27 ++++++++++++++++++++-------
  1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 35fb1f17a589c..4ad02ad640518 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1270,21 +1270,34 @@ static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
  	 * the read (except when CRS SV is enabled and the read was for the
  	 * Vendor ID; in that case it synthesizes 0x0001 data).
  	 *
-	 * Wait for the device to return a non-CRS completion.  Read the
-	 * Command register instead of Vendor ID so we don't have to
-	 * contend with the CRS SV value.
+	 * Wait for the device to return a non-CRS completion.  On devices
+	 * that support PM control and on waits that aren't part of system
+	 * resume read the PM control register to ensure the device has
+	 * transitioned to D0.  On devices that don't support PM control,
+	 * or during system resume read the command register to instead of
+	 * Vendor ID so we don't have to contend with the CRS SV value.
  	 */
  	for (;;) {
-		u32 id;
if (pci_dev_is_disconnected(dev)) {
  			pci_dbg(dev, "disconnected; not waiting\n");
  			return -ENOTTY;
  		}
- pci_read_config_dword(dev, PCI_COMMAND, &id);
-		if (!PCI_POSSIBLE_ERROR(id))
-			break;
+		if (dev->pm_cap && strcmp(reset_type, "resume") != 0) {

Comparing to a string makes me feel reset_type should be changed to
something that allows direct compare and those values only mapped into
string while printing it.


Thanks, that's a great suggestion. I'll add a patch earlier in the series to make an enum of the types instead and a mapping function for them to get the string as needed.




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