linux-kernel - Re: [PATCH v2] PCI/EDR: Clear PCIe Device Status errors after EDR error recovery

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Message-ID: <20230406210722.GA3735581@bhelgaas>
Date:   Thu, 6 Apr 2023 16:07:22 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI/EDR: Clear PCIe Device Status errors after EDR
 error recovery

On Wed, Mar 15, 2023 at 04:54:49PM -0700, Kuppuswamy Sathyanarayanan wrote:
> Commit 068c29a248b6 ("PCI/ERR: Clear PCIe Device Status errors only if
> OS owns AER") adds support to clear error status in the Device Status
> Register(DEVSTA) only if OS owns the AER support. But this change
> breaks the requirement of the EDR feature which requires OS to cleanup
> the error registers even if firmware owns the control of AER support.
> 
> More details about this requirement can be found in PCIe Firmware
> specification v3.3, Table 4-6 Interpretation of the _OSC Control Field.
> If the OS supports the Error Disconnect Recover (EDR) feature and
> firmware sends the EDR event, then during the EDR recovery window, OS
> is responsible for the device error recovery and holds the ownership of
> the following error registers.
> 
> • Device Status Register
> • Uncorrectable Error Status Register
> • Correctable Error Status Register
> • Root Error Status Register
> • RP PIO Status Register
> 
> So call pcie_clear_device_status() in edr_handle_event() if the error
> recovery is successful.
> 
> Reported-by: Tsaur Erwin <erwin.tsaur@...el.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---
> 
> Changes since v1:
>  * Rebased on top of v6.3-rc1.
>  * Fixed a typo in pcie_clear_device_status().
> 
>  drivers/pci/pcie/edr.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/pci/pcie/edr.c b/drivers/pci/pcie/edr.c
> index a6b9b479b97a..87734e4c3c20 100644
> --- a/drivers/pci/pcie/edr.c
> +++ b/drivers/pci/pcie/edr.c
> @@ -193,6 +193,7 @@ static void edr_handle_event(acpi_handle handle, u32 event, void *data)
>  	 */
>  	if (estate == PCI_ERS_RESULT_RECOVERED) {
>  		pci_dbg(edev, "DPC port successfully recovered\n");
> +		pcie_clear_device_status(edev);
>  		acpi_send_edr_status(pdev, edev, EDR_OST_SUCCESS);

The implementation note in PCI Firmware r3.3, sec 4.6.12, shows the OS
clearing error status *after* _OST is evaluated.

On the other hand, the _OSC DPC control bit in table 4-6 says that if
the OS does not have DPC control, it can only write the Device Status
error bits between the EDR Notify and invoking _OST.

Is one of those wrong, or am I missing something?

Bjorn