linux-kernel - Re: [PATCH] PCI AER: handle pci_cleanup_aer_uncorrect_error

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Date:	Fri, 13 Dec 2013 15:35:15 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Betty Dall <betty.dall@...com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] PCI AER: handle pci_cleanup_aer_uncorrect_error_status()
 in firmware first mode

On Fri, Dec 13, 2013 at 8:41 AM, Betty Dall <betty.dall@...com> wrote:
> There are three functions exported from aerdrv_core.c that could be
> called when the system is in firmware first mode:
> pci_enable_pcie_error_reporting(), pci_disable_pcie_error_reporting, and
> pci_cleanup_aer_uncorrect_error_status(). The first two functions check if
> we are in firmware first mode and return immediately.
> pci_cleanup_aer_uncorrect_error_status() does not check firmware first
> mode. The problem is that all of these functions should not access the AER
> registers in firmware first mode because the firmware has not granted OS
> control of the AER registers through the _OSC.

This looks like a good fix to me.  If I read aer_acpi_firmware_first()
correctly, we don't even *ask* for control of AER if
ACPI_HEST_FIRMWARE_FIRST appears anywhere in the HEST.  Does that
match your understanding?

> Many drivers call this
> function in their pci_error_handlers in firmware first mode.

Drivers don't have any idea whether their device is in firmware-first
mode, do they?

> The fix is to change pci_cleanup_aer_uncorrect_error_status() to check
> firmware first mode before accessing the AER registers. If it is in firmware
> first mode, return 0. I considered returning -EIO, but decided the status
> has been cleaned up appropriately for firmware first. Returning 0 also avoids
> an error message. Not many places check the return of this function, and the
> ones that do, print an error message and continue such as:
>    err = pci_cleanup_aer_uncorrect_error_status(pdev);
>    if (err) {
>        dev_err(&pdev->dev,
>            "pci_cleanup_aer_uncorrect_error_status failed 0x%0x\n",
>             err); /* non-fatal, continue */
>    }
> That error message is how I found this problem, and it is not applicable
> for the firmware first recovery path.

I'm curious -- did you find this problem because you saw a message
when pci_cleanup_aer_uncorrect_error_status() returned failure?  The
only way it can return failure is if there is no AER capability, and
that should be completely independent of whether we're in
firmware-first mode.

> Signed-off-by: Betty Dall <betty.dall@...com>
> ---
>
>  drivers/pci/pcie/aer/aerdrv_core.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
>
> diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c
> index b2c8881..1f60408 100644
> --- a/drivers/pci/pcie/aer/aerdrv_core.c
> +++ b/drivers/pci/pcie/aer/aerdrv_core.c
> @@ -62,6 +62,9 @@ int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev)
>         int pos;
>         u32 status;
>
> +       if (pcie_aer_get_firmware_first(dev))
> +               return 0;
> +
>         pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ERR);
>         if (!pos)
>                 return -EIO;
--
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