PCI/ASPM: Save L1 PM Substates Capability for suspend/resume

4ff116d0 ("PCI/ASPM: Save L1 PM Substates Capability for
suspend/resume") restored the L1 PM Substates Capability after resume,
which reduced power consumption by making the ASPM L1.x states work after
resume.

a7152be7 ("Revert "PCI/ASPM: Save L1 PM Substates Capability for
suspend/resume"") reverted 4ff116d0 because resume failed on some
systems, so power consumption after resume increased again.

a7152be7 mentioned that we restore L1 PM substate configuration even
though ASPM L1 may already be enabled. This is due the fact that the
pci_restore_aspm_l1ss_state() was called before pci_restore_pcie_state().

Save and restore the L1 PM Substates Capability, following PCIe r6.1, sec
5.5.4 more closely by:

  1) Do not restore ASPM configuration in pci_restore_pcie_state() but
     do that after PCIe capability is restored in pci_restore_aspm_state()
     following PCIe r6.1, sec 5.5.4.

  2) If BIOS reenables L1SS, particularly L1.2, we need to clear the
     enables in the right order, downstream before upstream. Defer
     restoring the L1SS config until we are at the downstream component.
     Then update the config for both ends of the link in the prescribed
     order.

  3) Program ASPM L1 PM substate configuration before L1 enables.

  4) Program ASPM L1 PM substate enables last, after rest of the fields
     in the capability are programmed.

[bhelgaas: commit log, squash L1SS-related patches, do both LNKCTL restores
in pci_restore_pcie_state()]

Link: https://lore.kernel.org/r/20240128233212.1139663-3-david.e.box@linux.intel.com
Link: https://lore.kernel.org/r/20240128233212.1139663-4-david.e.box@linux.intel.com
Link: https://lore.kernel.org/r/20240223205851.114931-5-helgaas@kernel.org
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217321
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216782
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216877Co-developed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Co-developed-by: David E. Box <david.e.box@linux.intel.com>
Reported-by: Koba Ko <koba.ko@canonical.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Tasev Nikola <tasev.stefanoska@skynet.be> # Asus UX305FA
Cc: Mark Enriquez <enriquezmark36@gmail.com>
Cc: Thomas Witt <kernel@witt.link>
Cc: Werner Sembach <wse@tuxedocomputers.com>
Cc: Vidya Sagar <vidyas@nvidia.com>

drivers/pci/pci.c

@@ -1623,6 +1623,8 @@ static int pci_save_pcie_state(struct pci_dev *dev)
 	pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &cap[i++]);
 	pcie_capability_read_word(dev, PCI_EXP_SLTCTL2, &cap[i++]);
 
+	pci_save_aspm_l1ss_state(dev);
+
 	return 0;
 }
 
@@ -1630,7 +1632,7 @@ static void pci_restore_pcie_state(struct pci_dev *dev)
 {
 	int i = 0;
 	struct pci_cap_saved_state *save_state;
-	u16 *cap;
+	u16 *cap, lnkctl;
 
 	save_state = pci_find_saved_cap(dev, PCI_CAP_ID_EXP);
 	if (!save_state)
@@ -1645,12 +1647,23 @@ static void pci_restore_pcie_state(struct pci_dev *dev)
 
 	cap = (u16 *)&save_state->cap.data[0];
 	pcie_capability_write_word(dev, PCI_EXP_DEVCTL, cap[i++]);
-	pcie_capability_write_word(dev, PCI_EXP_LNKCTL, cap[i++]);
+
+	/* Restore LNKCTL register with ASPM control field clear */
+	lnkctl = cap[i++];
+	pcie_capability_write_word(dev, PCI_EXP_LNKCTL,
+				   lnkctl & ~PCI_EXP_LNKCTL_ASPMC);
+
 	pcie_capability_write_word(dev, PCI_EXP_SLTCTL, cap[i++]);
 	pcie_capability_write_word(dev, PCI_EXP_RTCTL, cap[i++]);
 	pcie_capability_write_word(dev, PCI_EXP_DEVCTL2, cap[i++]);
 	pcie_capability_write_word(dev, PCI_EXP_LNKCTL2, cap[i++]);
 	pcie_capability_write_word(dev, PCI_EXP_SLTCTL2, cap[i++]);
+
+	pci_restore_aspm_l1ss_state(dev);
+
+	/* Restore ASPM control after restoring L1SS state */
+	pcie_capability_set_word(dev, PCI_EXP_LNKCTL,
+				 lnkctl & PCI_EXP_LNKCTL_ASPMC);
 }
 
 static int pci_save_pcix_state(struct pci_dev *dev)

drivers/pci/pci.h

@@ -571,6 +571,9 @@ int pcie_retrain_link(struct pci_dev *pdev, bool use_lt);
 /* ASPM-related functionality we need even without CONFIG_PCIEASPM */
 void pci_save_ltr_state(struct pci_dev *dev);
 void pci_restore_ltr_state(struct pci_dev *dev);
+void pci_configure_aspm_l1ss(struct pci_dev *dev);
+void pci_save_aspm_l1ss_state(struct pci_dev *dev);
+void pci_restore_aspm_l1ss_state(struct pci_dev *dev);
 
 #ifdef CONFIG_PCIEASPM
 void pcie_aspm_init_link_state(struct pci_dev *pdev);

drivers/pci/pcie/aspm.c

@@ -64,6 +64,105 @@ void pci_restore_ltr_state(struct pci_dev *dev)
 	pci_write_config_dword(dev, ltr + PCI_LTR_MAX_SNOOP_LAT, *cap);
 }
 
+void pci_configure_aspm_l1ss(struct pci_dev *pdev)
+{
+	int rc;
+
+	pdev->l1ss = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_L1SS);
+
+	rc = pci_add_ext_cap_save_buffer(pdev, PCI_EXT_CAP_ID_L1SS,
+					 2 * sizeof(u32));
+	if (rc)
+		pci_err(pdev, "unable to allocate ASPM L1SS save buffer (%pe)\n",
+			ERR_PTR(rc));
+}
+
+void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
+{
+	struct pci_cap_saved_state *save_state;
+	u16 l1ss = pdev->l1ss;
+	u32 *cap;
+
+	/*
+	 * Save L1 substate configuration. The ASPM L0s/L1 configuration
+	 * in PCI_EXP_LNKCTL_ASPMC is saved by pci_save_pcie_state().
+	 */
+	if (!l1ss)
+		return;
+
+	save_state = pci_find_saved_ext_cap(pdev, PCI_EXT_CAP_ID_L1SS);
+	if (!save_state)
+		return;
+
+	cap = &save_state->cap.data[0];
+	pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL2, cap++);
+	pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL1, cap++);
+}
+
+void pci_restore_aspm_l1ss_state(struct pci_dev *pdev)
+{
+	struct pci_cap_saved_state *pl_save_state, *cl_save_state;
+	struct pci_dev *parent = pdev->bus->self;
+	u32 *cap, pl_ctl1, pl_ctl2, pl_l1_2_enable;
+	u32 cl_ctl1, cl_ctl2, cl_l1_2_enable;
+
+	/*
+	 * In case BIOS enabled L1.2 when resuming, we need to disable it first
+	 * on the downstream component before the upstream. So, don't attempt to
+	 * restore either until we are at the downstream component.
+	 */
+	if (pcie_downstream_port(pdev) || !parent)
+		return;
+
+	if (!pdev->l1ss || !parent->l1ss)
+		return;
+
+	cl_save_state = pci_find_saved_ext_cap(pdev, PCI_EXT_CAP_ID_L1SS);
+	pl_save_state = pci_find_saved_ext_cap(parent, PCI_EXT_CAP_ID_L1SS);
+	if (!cl_save_state || !pl_save_state)
+		return;
+
+	cap = &cl_save_state->cap.data[0];
+	cl_ctl2 = *cap++;
+	cl_ctl1 = *cap;
+	cap = &pl_save_state->cap.data[0];
+	pl_ctl2 = *cap++;
+	pl_ctl1 = *cap;
+
+	/*
+	 * Disable L1.2 on this downstream endpoint device first, followed
+	 * by the upstream
+	 */
+	pci_clear_and_set_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL1,
+				       PCI_L1SS_CTL1_L1_2_MASK, 0);
+	pci_clear_and_set_config_dword(parent, parent->l1ss + PCI_L1SS_CTL1,
+				       PCI_L1SS_CTL1_L1_2_MASK, 0);
+
+	/*
+	 * In addition, Common_Mode_Restore_Time and LTR_L1.2_THRESHOLD
+	 * in PCI_L1SS_CTL1 must be programmed *before* setting the L1.2
+	 * enable bits, even though they're all in PCI_L1SS_CTL1.
+	 */
+	pl_l1_2_enable = pl_ctl1 & PCI_L1SS_CTL1_L1_2_MASK;
+	pl_ctl1 &= ~PCI_L1SS_CTL1_L1_2_MASK;
+	cl_l1_2_enable = cl_ctl1 & PCI_L1SS_CTL1_L1_2_MASK;
+	cl_ctl1 &= ~PCI_L1SS_CTL1_L1_2_MASK;
+
+	/* Write back without enables first (above we cleared them in ctl1) */
+	pci_write_config_dword(parent, parent->l1ss + PCI_L1SS_CTL2, pl_ctl2);
+	pci_write_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL2, cl_ctl2);
+	pci_write_config_dword(parent, parent->l1ss + PCI_L1SS_CTL1, pl_ctl1);
+	pci_write_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL1, cl_ctl1);
+
+	/* Then write back the enables */
+	if (pl_l1_2_enable || cl_l1_2_enable) {
+		pci_write_config_dword(parent, parent->l1ss + PCI_L1SS_CTL1,
+				       pl_ctl1 | pl_l1_2_enable);
+		pci_write_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL1,
+				       cl_ctl1 | cl_l1_2_enable);
+	}
+}
+
 #ifdef CONFIG_PCIEASPM
 
 #ifdef MODULE_PARAM_PREFIX
@@ -1005,9 +1104,6 @@ void pci_configure_ltr(struct pci_dev *pdev)
 	if (!pci_is_pcie(pdev))
 		return;
 
-	/* Read L1 PM substate capabilities */
-	pdev->l1ss = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_L1SS);
-
 	pcie_capability_read_dword(pdev, PCI_EXP_DEVCAP2, &cap);
 	if (!(cap & PCI_EXP_DEVCAP2_LTR))
 		return;

drivers/pci/probe.c

@@ -2259,6 +2259,7 @@ static void pci_configure_device(struct pci_dev *dev)
 	pci_configure_extended_tags(dev, NULL);
 	pci_configure_relaxed_ordering(dev);
 	pci_configure_ltr(dev);
+	pci_configure_aspm_l1ss(dev);
 	pci_configure_eetlp_prefix(dev);
 	pci_configure_serr(dev);
 

include/linux/pci.h

@@ -390,9 +390,9 @@ struct pci_dev {
 	unsigned int	d3hot_delay;	/* D3hot->D0 transition time in ms */
 	unsigned int	d3cold_delay;	/* D3cold->D0 transition time in ms */
 
+	u16		l1ss;		/* L1SS Capability pointer */
 #ifdef CONFIG_PCIEASPM
 	struct pcie_link_state	*link_state;	/* ASPM link state */
-	u16		l1ss;		/* L1SS Capability pointer */
 	unsigned int	ltr_path:1;	/* Latency Tolerance Reporting
 					   supported from root to here */
 #endif