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

[Mario Limonciello]

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.