Fwd: upstream linux cannot achieve package C8 power saving

[Bagas Sanjaya <bagasdotme@gmail.com>]

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Hi,

I notice a bug report on Bugzilla [1]. Quoting from it:

> v6.5 (and at least v5.15, v5.19 and v6.4 as well) will not go to a higher power saving level than package C3.
> 
> With the inclusion of a patch that combines 3 Ubuntu commits related to VMD ASPM & LTR, package C8 is used.

See Bugzilla for the full thread.

FYI, the attached proposed fix is the same as Brett's another BZ report [2].
I include it for upstreaming.

To Brett: Would you like to submit the proper, formal patch (see
Documentation/process/submitting-patches.rst for details)?

Thanks.

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=217841
[2]: https://bugzilla.kernel.org/show_bug.cgi?id=217828

-- 
An old man doll... just what I always wanted! - Clara

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commit 9491bfa0b1e5f658e09135759e7ebc373d9a72ce
Author: brett.hassall <brett.hassall@gmail.com>
Date:   Thu Aug 24 19:26:36 2023 +1000

    combined commit of: 71315b8e - UBUNTU: SAUCE: PCI/ASPM: Enable ASPM for links under VMD domain; d83e6f6e -  UBUNTU: SAUCE: PCI/ASPM: Enable LTR for endpoints behind VMD; 069d0523 - UBUNTU: SAUCE: vmd: fixup bridge ASPM by driver name instead

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 66d7514ca111..29f2f62aaefa 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -682,7 +682,8 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 	aspm_l1ss_init(link);
 
 	/* Save default state */
-	link->aspm_default = link->aspm_enabled;
+	link->aspm_default = parent->dev_flags & PCI_DEV_FLAGS_ENABLE_ASPM ?
+			     ASPM_STATE_ALL : link->aspm_enabled;
 
 	/* Setup initial capable state. Will be updated later */
 	link->aspm_capable = link->aspm_support;
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index c525867760bf..a77e2e38fa6a 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -6041,3 +6041,71 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x9a2d, dpc_log_size);
 DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x9a2f, dpc_log_size);
 DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x9a31, dpc_log_size);
 #endif
+
+/*
+ * BIOS may not be able to access config space of devices under VMD domain, so
+ * it relies on software to enable ASPM for links under VMD.
+ */
+static bool pci_fixup_is_vmd_bridge(struct pci_dev *pdev)
+{
+	struct pci_bus *bus = pdev->bus;
+	struct device *dev;
+	struct pci_driver *pdrv;
+
+	if (!pci_is_root_bus(bus))
+		return false;
+
+	dev = bus->bridge->parent;
+	if (dev == NULL)
+		return false;
+
+	pdrv = pci_dev_driver(to_pci_dev(dev));
+	if (pdrv == NULL || strcmp("vmd", pdrv->name))
+		return false;
+
+	return true;
+}
+
+static void pci_fixup_enable_aspm(struct pci_dev *pdev)
+{
+	if (!pci_fixup_is_vmd_bridge(pdev))
+		return;
+
+	pdev->dev_flags |= PCI_DEV_FLAGS_ENABLE_ASPM;
+	pci_info(pdev, "enable ASPM for pci bridge behind vmd");
+}
+DECLARE_PCI_FIXUP_CLASS_HEADER(PCI_VENDOR_ID_INTEL, PCI_ANY_ID,
+			       PCI_CLASS_BRIDGE_PCI, 8, pci_fixup_enable_aspm);
+
+static void pci_fixup_enable_vmd_nvme_ltr(struct pci_dev *pdev)
+{
+	struct pci_dev *parent;
+	int pos;
+	u16 val;
+
+	parent = pci_upstream_bridge(pdev);
+	if (!parent)
+		return;
+
+	if (!pci_fixup_is_vmd_bridge(parent))
+		return;
+
+	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_LTR);
+	if (!pos)
+		return;
+
+	pci_read_config_word(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, &val);
+	if (val)
+		return;
+
+	pci_read_config_word(pdev, pos + PCI_LTR_MAX_NOSNOOP_LAT, &val);
+	if (val)
+		return;
+
+	/* 3145728ns, i.e. 0x300000ns */
+	pci_write_config_word(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, 0x1003);
+	pci_write_config_word(pdev, pos + PCI_LTR_MAX_NOSNOOP_LAT, 0x1003);
+	pci_info(pdev, "enable LTR for nvme behind vmd");
+}
+DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_ANY_ID, PCI_ANY_ID,
+			      PCI_CLASS_STORAGE_EXPRESS, 0, pci_fixup_enable_vmd_nvme_ltr);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 60b8772b5bd4..d3f96d111250 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -245,6 +245,8 @@ enum pci_dev_flags {
 	PCI_DEV_FLAGS_NO_RELAXED_ORDERING = (__force pci_dev_flags_t) (1 << 11),
 	/* Device does honor MSI masking despite saying otherwise */
 	PCI_DEV_FLAGS_HAS_MSI_MASKING = (__force pci_dev_flags_t) (1 << 12),
+	/* Enable ASPM regardless of how LnkCtl is programmed */
+	PCI_DEV_FLAGS_ENABLE_ASPM = (__force pci_dev_flags_t) (1 << 13),
 };
 
 enum pci_irq_reroute_variant {