[PATCH V4 2/2] PCI: vmd: Override ASPM on TGL/ADL VMD devices

["David E. Box" <david.e.box@linux.intel.com>]

From: Michael Bottini <michael.a.bottini@linux.intel.com>

On Tiger Lake and Alder Lake platforms, VMD controllers do not have ASPM
enabled nor LTR values set by BIOS. This leads high power consumption on
these platforms when VMD is enabled as reported in bugzilla [1].  Enable
these features in the VMD driver using pcie_aspm_policy_override() to set
the ASPM policy for the root ports.

To do this, add an additional flag in VMD features to specify devices that
must have their respective policies overridden.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=213717

Signed-off-by: Michael Bottini <michael.a.bottini@linux.intel.com>
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Tested-by: Adhitya Mohan <me@adhityamohan.in>
---
V4
 - Refactor vmd_enable_apsm() to exit early, making the lines shorter
   and more readable. Suggested by Christoph.
V3
 - No changes
V2
 - Use return status to print pci_info message if ASPM cannot be enabled.
 - Add missing static declaration, caught by lkp@intel.com

 drivers/pci/controller/vmd.c | 43 +++++++++++++++++++++++++++++++++---
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index a45e8e59d3d4..880afd450a14 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -20,6 +20,8 @@
 
 #include <asm/irqdomain.h>
 
+#include "../pci.h"
+
 #define VMD_CFGBAR	0
 #define VMD_MEMBAR1	2
 #define VMD_MEMBAR2	4
@@ -67,6 +69,12 @@ enum vmd_features {
 	 * interrupt handling.
 	 */
 	VMD_FEAT_CAN_BYPASS_MSI_REMAP		= (1 << 4),
+
+	/*
+	 * Device must have ASPM policy overridden, as its default policy is
+	 * incorrect.
+	 */
+	VMD_FEAT_QUIRK_OVERRIDE_ASPM		= (1 << 5),
 };
 
 static DEFINE_IDA(vmd_instance_ida);
@@ -661,6 +669,30 @@ static int vmd_alloc_irqs(struct vmd_dev *vmd)
 	return 0;
 }
 
+/*
+ * Override the BIOS ASPM policy and set the LTR value for PCI storage
+ * devices on the VMD bride.
+ */
+static int vmd_enable_aspm(struct pci_dev *pdev, void *userdata)
+{
+	int features = *(int *)userdata, pos;
+
+	if (!(features & VMD_FEAT_QUIRK_OVERRIDE_ASPM) ||
+	    pdev->class != PCI_CLASS_STORAGE_EXPRESS)
+		return 0;
+
+	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_LTR);
+	if (!pos)
+		return 0;
+
+	pci_write_config_word(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, 0x1003);
+	pci_write_config_word(pdev, pos + PCI_LTR_MAX_NOSNOOP_LAT, 0x1003);
+	if (pcie_aspm_policy_override(pdev))
+		pci_info(pdev, "Unable of override ASPM policy\n");
+
+	return 0;
+}
+
 static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
 {
 	struct pci_sysdata *sd = &vmd->sysdata;
@@ -807,6 +839,8 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
 	pci_scan_child_bus(vmd->bus);
 	pci_assign_unassigned_bus_resources(vmd->bus);
 
+	pci_walk_bus(vmd->bus, vmd_enable_aspm, &features);
+
 	/*
 	 * VMD root buses are virtual and don't return true on pci_is_pcie()
 	 * and will fail pcie_bus_configure_settings() early. It can instead be
@@ -948,15 +982,18 @@ static const struct pci_device_id vmd_ids[] = {
 	{PCI_DEVICE(PCI_VENDOR_ID_INTEL, 0x467f),
 		.driver_data = VMD_FEAT_HAS_MEMBAR_SHADOW_VSCAP |
 				VMD_FEAT_HAS_BUS_RESTRICTIONS |
-				VMD_FEAT_OFFSET_FIRST_VECTOR,},
+				VMD_FEAT_OFFSET_FIRST_VECTOR |
+				VMD_FEAT_QUIRK_OVERRIDE_ASPM,},
 	{PCI_DEVICE(PCI_VENDOR_ID_INTEL, 0x4c3d),
 		.driver_data = VMD_FEAT_HAS_MEMBAR_SHADOW_VSCAP |
 				VMD_FEAT_HAS_BUS_RESTRICTIONS |
-				VMD_FEAT_OFFSET_FIRST_VECTOR,},
+				VMD_FEAT_OFFSET_FIRST_VECTOR |
+				VMD_FEAT_QUIRK_OVERRIDE_ASPM,},
 	{PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_VMD_9A0B),
 		.driver_data = VMD_FEAT_HAS_MEMBAR_SHADOW_VSCAP |
 				VMD_FEAT_HAS_BUS_RESTRICTIONS |
-				VMD_FEAT_OFFSET_FIRST_VECTOR,},
+				VMD_FEAT_OFFSET_FIRST_VECTOR |
+				VMD_FEAT_QUIRK_OVERRIDE_ASPM,},
 	{0,}
 };
 MODULE_DEVICE_TABLE(pci, vmd_ids);
-- 
2.25.1