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

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Wed, 10 Jul 2024, superm1@kernel.org wrote:

> From: Mario Limonciello <mario.limonciello@amd.com>
> 
> 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@amd.com>
> ---
>  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.

-- 
 i.

> +			u16 pmcsr;
> +
> +			pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
> +			if (!PCI_POSSIBLE_ERROR(pmcsr) &&
> +			    (pmcsr & PCI_PM_CTRL_STATE_MASK) == PCI_D0)
> +				break;
> +		} else {
> +			u32 id;
> +
> +			pci_read_config_dword(dev, PCI_COMMAND, &id);
> +			if (!PCI_POSSIBLE_ERROR(id))
> +				break;
> +		}
>  
>  		if (delay > timeout) {
>  			pci_warn(dev, "not ready %dms after %s; giving up\n",
>