linux-kernel - Re: [RFC][PATCH 1/4] PCI PM: Add function for checking PME status of devices

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Message-Id: <200910081732.03157.bjorn.helgaas@hp.com>
Date:	Thu, 8 Oct 2009 17:32:02 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linux PCI <linux-pci@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Shaohua Li <shaohua.li@...el.com>
Subject: Re: [RFC][PATCH 1/4] PCI PM: Add function for checking PME status of devices

On Thursday 08 October 2009 04:52:48 pm Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> Add function pci_check_pme_status() that will check the PME status
> bit of given device and clear it along with the PME enable bit.  It
> will be necessary for PCI run-time power management.
> 
> Based on a patch from Shaohua Li <shaohua.li@...el.com>
> 
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> ---
>  drivers/pci/pci.c |   35 +++++++++++++++++++++++++++++++++++
>  drivers/pci/pci.h |    1 +
>  2 files changed, 36 insertions(+)
> 
> Index: linux-2.6/drivers/pci/pci.h
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pci.h
> +++ linux-2.6/drivers/pci/pci.h
> @@ -49,6 +49,7 @@ struct pci_platform_pm_ops {
>  extern int pci_set_platform_pm(struct pci_platform_pm_ops *ops);
>  extern void pci_update_current_state(struct pci_dev *dev, pci_power_t state);
>  extern void pci_disable_enabled_device(struct pci_dev *dev);
> +extern bool pci_check_pme_status(struct pci_dev *dev);
>  extern void pci_pm_init(struct pci_dev *dev);
>  extern void platform_pci_wakeup_init(struct pci_dev *dev);
>  extern void pci_allocate_cap_save_buffers(struct pci_dev *dev);
> Index: linux-2.6/drivers/pci/pci.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pci.c
> +++ linux-2.6/drivers/pci/pci.c
> @@ -1167,6 +1167,41 @@ int pci_set_pcie_reset_state(struct pci_
>  }
>  
>  /**
> + * pci_check_pme_status - Check if given device has generated PME.
> + * @dev: Device to check.
> + *
> + * Check the PME status of the device, clear PME status and PME enable.  Return
> + * 'true' if PME has been generated by the device (and hasn't been spurious) or
> + * 'false' otherwise.

This comment confuses me because it implies that we always clear PME enable,
but that's not what the code does.  If PME_STATUS is not asserted, the code
doesn't write anything.

> + */
> +bool pci_check_pme_status(struct pci_dev *dev)
> +{
> +	int pmcsr_pos;
> +	u16 pmcsr;
> +	bool ret = false;
> +
> +	if (!dev->pm_cap)
> +		return false;
> +
> +	pmcsr_pos = dev->pm_cap + PCI_PM_CTRL;
> +	/* clear PME status and disable PME to avoid interrupt flood */
> +	pci_read_config_word(dev, pmcsr_pos, &pmcsr);
> +	if (!(pmcsr & PCI_PM_CTRL_PME_STATUS))
> +		return false;
> +
> +	pmcsr |= PCI_PM_CTRL_PME_STATUS;
> +	/* Ignore spurious PME or clear PME enable if it's not spurious. */
> +	if (pmcsr & PCI_PM_CTRL_PME_ENABLE) {
> +		pmcsr &= ~PCI_PM_CTRL_PME_ENABLE;
> +		ret = true;
> +	}
> +
> +	pci_write_config_word(dev, pmcsr_pos, pmcsr);

I can't tell whether the comment or the code is what was intended,
but I think the following would be a clearer way to implement the
comment:

	pci_read_config_word(..., &pmcsr);
	pci_write_config_word(..., (pmcsr | STATUS) & ~ENABLE);

	if ((pmcsr & ENABLE) && (pmcsr & STATUS))
		return true;
	return false;

Bjorn

> +
> +	return ret;
> +}
> +
> +/**
>   * pci_pme_capable - check the capability of PCI device to generate PME#
>   * @dev: PCI device to handle.
>   * @state: PCI state from which device will issue PME#.
> 


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