[PATCH] AER: aer_root_reset() non-native handling

[Sean V Kelley <sean.v.kelley@xxxxxxxxx>]

If an OS has not been granted AER control via _OSC, then
the OS should not make changes to PCI_ERR_ROOT_COMMAND and
PCI_ERR_ROOT_STATUS related registers. Per section 4.5.1 of
the System Firmware Intermediary (SFI) _OSC and DPC Updates
ECN [1], this bit also covers these aspects of the PCI
Express Advanced Error Reporting. Further, the handling of
clear/enable of PCI_ERROR_ROOT_COMMAND when wrapped around
PCI_ERR_ROOT_STATUS should have no effect and be removed.
Based on the above and earlier discussion [2], make the
following changes:

Add a check for the native case (i.e., AER control via _OSC)
Re-order and remove some of the handling:
- clear PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK
- do reset
- clear PCI_ERR_ROOT_STATUS
- enable PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK

to this:

- clear PCI_ERR_ROOT_STATUS
- do reset

The current "clear, reset, enable" order suggests that the reset
might cause errors that we should ignore. But I am unable to find a
reference and the clearing of PCI_ERR_ROOT_STATUS does not require them.

[1] System Firmware Intermediary (SFI) _OSC and DPC Updates ECN, Feb 24,
    2020, affecting PCI Firmware Specification, Rev. 3.2
    https://members.pcisig.com/wg/PCI-SIG/document/14076
[2] https://lore.kernel.org/linux-pci/20201020162820.GA370938@bjorn-Precision-5520/

Signed-off-by: Sean V Kelley <sean.v.kelley@xxxxxxxxx>
---
 drivers/pci/pcie/aer.c | 21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
index 65dff5f3457a..bbfb07842d89 100644
--- a/drivers/pci/pcie/aer.c
+++ b/drivers/pci/pcie/aer.c
@@ -1361,23 +1361,14 @@ static pci_ers_result_t aer_root_reset(struct pci_dev *dev)
 	u32 reg32;
 	int rc;
 
-
-	/* Disable Root's interrupt in response to error messages */
-	pci_read_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, &reg32);
-	reg32 &= ~ROOT_PORT_INTR_ON_MESG_MASK;
-	pci_write_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, reg32);
+	if (pcie_aer_is_native(dev)) {
+		/* Clear Root Error Status */
+		pci_read_config_dword(dev, aer + PCI_ERR_ROOT_STATUS, &reg32);
+		pci_write_config_dword(dev, aer + PCI_ERR_ROOT_STATUS, reg32);
+	}
 
 	rc = pci_bus_error_reset(dev);
-	pci_info(dev, "Root Port link has been reset\n");
-
-	/* Clear Root Error Status */
-	pci_read_config_dword(dev, aer + PCI_ERR_ROOT_STATUS, &reg32);
-	pci_write_config_dword(dev, aer + PCI_ERR_ROOT_STATUS, reg32);
-
-	/* Enable Root Port's interrupt in response to error messages */
-	pci_read_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, &reg32);
-	reg32 |= ROOT_PORT_INTR_ON_MESG_MASK;
-	pci_write_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, reg32);
+	pci_info(dev, "Root Port link has been reset (%d)\n", rc);
 
 	return rc ? PCI_ERS_RESULT_DISCONNECT : PCI_ERS_RESULT_RECOVERED;
 }
-- 
2.29.2