linux-kernel - Re: [PATCH v4 2/5] PCI: Check PCI_PM_CTRL instead of PCI_COMMAND in pci_dev

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Message-ID: <764e053f-4d6c-14ab-b0f4-fac22f90bf2e@linux.intel.com>
Date: Fri, 23 Aug 2024 15:13:46 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Mario Limonciello <superm1@...nel.org>
cc: Bjorn Helgaas <bhelgaas@...gle.com>, 
    Mathias Nyman <mathias.nyman@...el.com>, 
    Mika Westerberg <mika.westerberg@...ux.intel.com>, 
    "open list : PCI SUBSYSTEM" <linux-pci@...r.kernel.org>, 
    open list <linux-kernel@...r.kernel.org>, 
    "open list : USB XHCI DRIVER" <linux-usb@...r.kernel.org>, 
    Daniel Drake <drake@...lessos.org>, Gary Li <Gary.Li@....com>, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v4 2/5] PCI: Check PCI_PM_CTRL instead of PCI_COMMAND in
 pci_dev_wait()

On Thu, 22 Aug 2024, Mario Limonciello wrote:

> From: Mario Limonciello <mario.limonciello@....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.

It feels part of the coverletter text would belong into this patch.

> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  drivers/pci/pci.c | 28 ++++++++++++++++++++--------
>  1 file changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e4a7f5dfe6bf4..b7717155e2fd0 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1308,21 +1308,33 @@ static int pci_dev_wait(struct pci_dev *dev, enum pci_reset_type reset_type, int
>  	 * 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 && reset_type != PCI_DEV_WAIT_RESUME) {
> +			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)

Misleading indentation.

-- 
 i.

> +				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",
>