linux-kernel - [PATCH V5 3/3] PCI: vmd: Configure PCIe ASPM and LTR

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Message-Id: <20220218045056.333799-4-david.e.box@linux.intel.com>
Date:   Thu, 17 Feb 2022 20:50:56 -0800
From:   "David E. Box" <david.e.box@...ux.intel.com>
To:     nirmal.patel@...ux.intel.com, jonathan.derrick@...ux.dev,
        lorenzo.pieralisi@....com, hch@...radead.org, kw@...ux.com,
        robh@...nel.org, bhelgaas@...gle.com, david.e.box@...ux.intel.com,
        michael.a.bottini@...ux.intel.com, rafael@...nel.org,
        me@...ityamohan.in
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH V5 3/3] PCI: vmd: Configure PCIe ASPM and LTR

Currently, PCIe ports reserved for VMD use are not visible to BIOS and
therefore not configured to enable PCIE ASPM. Additionally, PCIE LTR
values may be left unset since BIOS will set a default maximum LTR value
on endpoints to ensure that misconfigured devices don't block SoC power
management. Lack of this programming results in high power consumption
on laptops as reported in bugzilla [1].  For currently affected
products, use pci_enable_default_link_state to set the allowed link
states for devices on the root ports. Also set the LTR value to the
maximum value needed for the SoC. Per the VMD hardware team future
products using VMD will enable BIOS configuration of these capabilities.
This solution is a workaround for current products that mainly targets
laptops. Support is not provided if a switch is used nor for hotplug.

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

Signed-off-by: Michael Bottini <michael.a.bottini@...ux.intel.com>
Signed-off-by: David E. Box <david.e.box@...ux.intel.com>
---
V5
 - Provide the LTR value as driver data.
 - Use DWORD for the config space write to avoid PCI WORD access bug.
 - Set ASPM links firsts, enabling all link states, before setting a
   default LTR if the capability is present
 - Add kernel message that VMD is setting the device LTR.
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@...el.com

 drivers/pci/controller/vmd.c | 48 +++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index a582c351b461..eac379c80cd7 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -67,10 +67,19 @@ enum vmd_features {
 	 * interrupt handling.
 	 */
 	VMD_FEAT_CAN_BYPASS_MSI_REMAP		= (1 << 4),
+
+	/*
+	 * Enable ASPM on the PCIE root ports and set the default LTR of the
+	 * storage devices on platforms where these values are not configured by
+	 * BIOS. This is needed for laptops, which require these settings for
+	 * proper power management of the SoC.
+	 */
+	VMD_FEAT_BIOS_PM_QUIRK		= (1 << 5),
 };
 
 struct vmd_device_data {
 	enum vmd_features features;
+	u16 ltr;
 };
 
 static DEFINE_IDA(vmd_instance_ida);
@@ -714,6 +723,38 @@ static void vmd_copy_host_bridge_flags(struct pci_host_bridge *root_bridge,
 	vmd_bridge->native_dpc = root_bridge->native_dpc;
 }
 
+/*
+ * Enable ASPM and LTR settings on devices that aren't configured by BIOS.
+ */
+static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
+{
+	struct vmd_device_data *info = userdata;
+	u32 ltr_reg;
+	int pos;
+
+	if (!(info->features & VMD_FEAT_BIOS_PM_QUIRK))
+		return 0;
+
+	pci_enable_default_link_state(pdev, PCIE_LINK_STATE_ALL);
+
+	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_LTR);
+	if (!pos)
+		return 0;
+
+	/*
+	 * If the LTR capability is present, set the default values to the
+	 * maximum required by the platform to allow the deepest power
+	 * management savings. Write this as a single DWORD where the lower word
+	 * is the max snoop latency and the upper word is the max non-snoop
+	 * latency.
+	 */
+	pci_info(pdev, "VMD: Setting a default LTR\n");
+	ltr_reg = (info->ltr << 16) | info->ltr;
+	pci_write_config_dword(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, ltr_reg);
+
+	return 0;
+}
+
 static int vmd_enable_domain(struct vmd_dev *vmd, struct vmd_device_data *info)
 {
 	struct pci_sysdata *sd = &vmd->sysdata;
@@ -867,6 +908,8 @@ static int vmd_enable_domain(struct vmd_dev *vmd, struct vmd_device_data *info)
 		pci_reset_bus(child->self);
 	pci_assign_unassigned_bus_resources(vmd->bus);
 
+	pci_walk_bus(vmd->bus, vmd_pm_enable_quirk, info);
+
 	/*
 	 * 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
@@ -1012,7 +1055,10 @@ static const struct vmd_device_data vmd_28c0_data = {
 static const struct vmd_device_data vmd_467f_data = {
 	.features = VMD_FEAT_HAS_MEMBAR_SHADOW_VSCAP |
 		    VMD_FEAT_HAS_BUS_RESTRICTIONS |
-		    VMD_FEAT_OFFSET_FIRST_VECTOR,
+		    VMD_FEAT_OFFSET_FIRST_VECTOR |
+		    VMD_FEAT_BIOS_PM_QUIRK,
+	/* 3145728 ns (LatencyScale of 1048576 ns with a LatencyValue of 3) */
+	.ltr = 0x1003,
 };
 
 static const struct pci_device_id vmd_ids[] = {
-- 
2.25.1