PCI: Add pci_disable_parity()

Add pci_disable_parity() to disable reporting of parity errors for a
device by clearing PCI_COMMAND_PARITY.

The device will still set PCI_STATUS_DETECTED_PARITY when it detects
a parity error or receives a Poisoned TLP, but it will not set
PCI_STATUS_PARITY, which means it will not assert PERR#
(conventional PCI) or report Poisoned TLPs (PCIe).

Based-on: https://lore.kernel.org/linux-arm-kernel/d375987c-ea4f-dd98-4ef8-99b2fbfe7c33@gmail.com/Based-on-patch-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/20210330174318.1289680-2-helgaas@kernel.orgSigned-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pci.c

@@ -4453,6 +4453,23 @@ void pci_clear_mwi(struct pci_dev *dev)
 }
 EXPORT_SYMBOL(pci_clear_mwi);
 
+/**
+ * pci_disable_parity - disable parity checking for device
+ * @dev: the PCI device to operate on
+ *
+ * Disable parity checking for device @dev
+ */
+void pci_disable_parity(struct pci_dev *dev)
+{
+	u16 cmd;
+
+	pci_read_config_word(dev, PCI_COMMAND, &cmd);
+	if (cmd & PCI_COMMAND_PARITY) {
+		cmd &= ~PCI_COMMAND_PARITY;
+		pci_write_config_word(dev, PCI_COMMAND, cmd);
+	}
+}
+
 /**
  * pci_intx - enables/disables PCI INTx for device dev
  * @pdev: the PCI device to operate on

include/linux/pci.h

@@ -1201,6 +1201,7 @@ int __must_check pci_set_mwi(struct pci_dev *dev);
 int __must_check pcim_set_mwi(struct pci_dev *dev);
 int pci_try_set_mwi(struct pci_dev *dev);
 void pci_clear_mwi(struct pci_dev *dev);
+void pci_disable_parity(struct pci_dev *dev);
 void pci_intx(struct pci_dev *dev, int enable);
 bool pci_check_and_mask_intx(struct pci_dev *dev);
 bool pci_check_and_unmask_intx(struct pci_dev *dev);