[PATCH V8 02/15] PCI: Disable MSI for Tegra194 root port

[Vidya Sagar]

Tegra194 rootports don't generate MSI interrupts for PME and AER events.
Since PCIe spec (Ref: r4.0 sec 7.7.1.2 and 7.7.2.2) doesn't support using
a mix of INTx and MSI/MSI-X, MSI needs to be disabled to avoid root ports
service drivers registering their respective ISRs with MSI interrupt and
to let only INTx be used for all events.

Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
Reviewed-by: Thierry Reding <treding@xxxxxxxxxx>
---
Changes since [v7]:
* Changed quirk macro to consider class code as well to avoid this quirk
  getting applied to Tegra194 when it is operating in endpoint mode. Also
  quoted relevant sections from PCIe spec in comments.

Changes since [v6]:
* This is a new patch

 drivers/pci/quirks.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 0f16acc323c6..69c061e0ca7d 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -2592,6 +2592,29 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_NVIDIA,
 			PCI_DEVICE_ID_NVIDIA_NVENET_15,
 			nvenet_msi_disable);
 
+/*
+ * PCIe spec r4.0 sec 7.7.1.2 and sec 7.7.2.2 say that if MSI/MSI-X is enabled,
+ * then the device can't use INTx interrupts. Tegra194's PCIe root ports don't
+ * generate MSI interrupts for PME and AER events instead only INTx interrupts
+ * are generated. Though Tegra194 can generate MSI interrupts for other events,
+ * since PCIe specificiation doesn't support using a mix of INTx and MSI/MSI-X,
+ * it is required to disable MSI interrupts to avoid port service drivers
+ * registering their respective ISRs for MSIs.
+ */
+static void pci_quirk_nvidia_tegra194_disable_rp_msi(struct pci_dev *dev)
+{
+	dev->no_msi = 1;
+}
+DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_NVIDIA, 0x1ad0,
+			      PCI_CLASS_BRIDGE_PCI, 8,
+			      pci_quirk_nvidia_tegra194_disable_rp_msi);
+DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_NVIDIA, 0x1ad1,
+			      PCI_CLASS_BRIDGE_PCI, 8,
+			      pci_quirk_nvidia_tegra194_disable_rp_msi);
+DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_NVIDIA, 0x1ad2,
+			      PCI_CLASS_BRIDGE_PCI, 8,
+			      pci_quirk_nvidia_tegra194_disable_rp_msi);
+
 /*
  * Some versions of the MCP55 bridge from Nvidia have a legacy IRQ routing
  * config register.  This register controls the routing of legacy
-- 
2.17.1