PCI: vmd: Enable PCI PM's L1 substates of remapped PCIe Root Port and NVMe

Notice the VMD remapped PCIe Root Port and NVMe have PCI PM L1 substates capability, but they are disabled originally.

Here is a failed example on ASUS B1400CEAE with enabled VMD:

10000:e0:06.0 PCI bridge [0604]: Intel Corporation 11th Gen Core Processor PCIe Controller [8086:9a09] (rev 01) (prog-if 00 [Normal decode])

    ...
    Capabilities: [200 v1] L1 PM Substates
        L1SubCap: PCI-PM_L1.2+ PCI-PM_L1.1+ ASPM_L1.2+ ASPM_L1.1+ L1_PM_Substates+
                  PortCommonModeRestoreTime=45us PortTPowerOnTime=50us
        L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
                   T_CommonMode=0us LTR1.2_Threshold=0ns
        L1SubCtl2: T_PwrOn=0us

10000:e1:00.0 Non-Volatile memory controller [0108]: Sandisk Corp WD Blue SN550 NVMe SSD [15b7:5009] (rev 01) (prog-if 02 [NVM Express])

    ...
    Capabilities: [900 v1] L1 PM Substates
        L1SubCap: PCI-PM_L1.2+ PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1- L1_PM_Substates+
                  PortCommonModeRestoreTime=32us PortTPowerOnTime=10us
        L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
                   T_CommonMode=0us LTR1.2_Threshold=101376ns
        L1SubCtl2: T_PwrOn=50us

According to "PCIe r6.0, sec 5.5.4", to config the link between the PCIe Root Port and the child device correctly:
* Ensure both devices are in D0 before enabling PCI-PM L1 PM Substates.
* Ensure L1.2 parameters: Common_Mode_Restore_Times, T_POWER_ON and LTR_L1.2_THRESHOLD are programmed properly on both devices before enable bits for L1.2.

Prepare this series to fix that.

Jian-Hong Pan (3):
PCI: vmd: Set PCI devices to D0 before enable PCI PM's L1 substates PCI/ASPM: Add notes about enabling PCI-PM L1SS to
pci_enable_link_state(_locked)
PCI/ASPM: Make pci_save_aspm_l1ss_state save both child and parent's
L1SS configuration

 drivers/pci/controller/vmd.c | 13 +++++++++----
 drivers/pci/pcie/aspm.c      | 26 +++++++++++++++++++++++++-
 2 files changed, 34 insertions(+), 5 deletions(-)

2.46.2

The remapped PCIe Root Port and the child device have PCI PM L1 substates capability, but they are disabled originally.

Here is a failed example on ASUS B1400CEAE:

Capabilities: [900 v1] L1 PM Substates

	L1SubCap: PCI-PM_L1.2+ PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1- L1_PM_Substates+
		  PortCommonModeRestoreTime=32us PortTPowerOnTime=10us
	L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
		   T_CommonMode=0us LTR1.2_Threshold=101376ns
	L1SubCtl2: T_PwrOn=50us

Power on all of the VMD remapped PCI devices to D0 before enable PCI-PM L1 PM Substates by following "PCIe r6.0, sec 5.5.4".

---
v2:
- Power on the VMD remapped devices with pci_set_power_state_locked()
- Prepare the PCIe LTR parameters before enable L1 Substates
- Add note into the comments of both pci_enable_link_state() and pci_enable_link_state_locked() for kernel-doc.
- The original patch set can be split as individual patches.

v3:
- Re-send for the missed version information.
- Split drivers/pci/pcie/aspm.c modification into following patches.
- Fix the comment for enasuring the PCI devices in D0.

v4:
- The same

v5:
- Tweak the commit title and message
- Change the goto label from out_enable_link_state to out_state_change

v6~8:
- The same

v9:
- Update L1 PM Substates information against kernel v6.11 in commit message

v10~11:
- The same

 drivers/pci/controller/vmd.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

index 264a180403a0..11870d1fc818 100644
@@ -740,11 +740,9 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
 	if (!(features & VMD_FEAT_BIOS_PM_QUIRK))
 		return 0;
 
-	pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
-
 	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_LTR);
 	if (!pos)
-		return 0;
+		goto out_state_change;
 
 	/*
 	 * Skip if the max snoop LTR is non-zero, indicating BIOS has set it

@@ -752,7 +750,7 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
 	 */
 	pci_read_config_dword(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, &ltr_reg);
 	if (!!(ltr_reg & (PCI_LTR_VALUE_MASK | PCI_LTR_SCALE_MASK)))
-		return 0;
+		goto out_state_change;
 
 	/*
 	 * Set the default values to the maximum required by the platform to

@@ -764,6 +762,13 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
 	pci_write_config_dword(pdev, pos + PCI_LTR_MAX_SNOOP_LAT, ltr_reg);
 	pci_info(pdev, "VMD: Default LTR value set by driver\n");
 
+out_state_change:
+	/*
+	 * Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
+	 * PCIe r6.0, sec 5.5.4.
+	 */
+	pci_set_power_state_locked(pdev, PCI_D0);
+	pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
 	return 0;
 }
 

2.46.2

According to "PCIe r6.0, sec 5.5.4", add note about D0 requirement in pci_enable_link_state() kernel-doc.

---
v3:
- Fix as readable comments

v4:
- The same

v5:
- Tweak and simplify the commit message

v6~11:
- The same

 drivers/pci/pcie/aspm.c | 6 ++++++
 1 file changed, 6 insertions(+)

index cee2365e54b8..bd0a8a05647e 100644
@@ -1442,6 +1442,9 @@ static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
  * touch the LNKCTL register. Also note that this does not enable states
  * disabled by pci_disable_link_state(). Return 0 or a negative errno.
  *
+ * Note: Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
+ * PCIe r6.0, sec 5.5.4.
+ *
  * @pdev: PCI device
  * @state: Mask of ASPM link states to enable
  */

@@ -1458,6 +1461,9 @@ EXPORT_SYMBOL(pci_enable_link_state);
  * can't touch the LNKCTL register. Also note that this does not enable states
  * disabled by pci_disable_link_state(). Return 0 or a negative errno.
  *
+ * Note: Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
+ * PCIe r6.0, sec 5.5.4.
+ *
  * @pdev: PCI device
  * @state: Mask of ASPM link states to enable
  *

2.46.2

PCI devices' parameters on the VMD bus have been programmed properly originally. But, cleared after pci_reset_bus() and have not been restored correctly. This leads the link's L1.2 between PCIe Root Port and child device gets wrong configs.

Here is a failed example on ASUS B1400CEAE with enabled VMD. Both PCIe bridge and NVMe device should have the same LTR1.2_Threshold value. However, they are configured as different values in this case:

10000:e0:06.0 PCI bridge [0604]: Intel Corporation 11th Gen Core Processor PCIe Controller [8086:9a09] (rev 01) (prog-if 00 [Normal decode])
...
Capabilities: [200 v1] L1 PM Substates

    L1SubCap: PCI-PM_L1.2+ PCI-PM_L1.1+ ASPM_L1.2+ ASPM_L1.1+ L1_PM_Substates+
      PortCommonModeRestoreTime=45us PortTPowerOnTime=50us
    L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
      T_CommonMode=0us LTR1.2_Threshold=0ns
    L1SubCtl2: T_PwrOn=0us

10000:e1:00.0 Non-Volatile memory controller [0108]: Sandisk Corp WD Blue SN550 NVMe SSD [15b7:5009] (rev 01) (prog-if 02 [NVM Express])
...
Capabilities: [900 v1] L1 PM Substates

    L1SubCap: PCI-PM_L1.2+ PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1- L1_PM_Substates+
      PortCommonModeRestoreTime=32us PortTPowerOnTime=10us
    L1SubCtl1: PCI-PM_L1.2- PCI-PM_L1.1- ASPM_L1.2+ ASPM_L1.1-
      T_CommonMode=0us LTR1.2_Threshold=101376ns
    L1SubCtl2: T_PwrOn=50us

Here is VMD mapped PCI device tree:

-+-[0000:00]-+-00.0 Intel Corporation Device 9a04
| ...
\-[10000:e0]-+-06.0-[e1]----00.0 Sandisk Corp WD Blue SN550 NVMe SSD
\-17.0 Intel Corporation Tiger Lake-LP SATA Controller

When pci_reset_bus() resets the bus [e1] of the NVMe, it only saves and restores NVMe's state before and after reset. The bus [e1] has only one NVMe device, so the NVMe's parent PCIe bridge is missed to be saved. However, when it restores the NVMe's state, ASPM code restores L1SS for both the parent bridge and the NVMe in pci_restore_aspm_l1ss_state(). Although the NVMe's L1SS is restored correctly, the parent bridge's L1SS is restored with a wrong value 0x0. Because, the parent bridge's L1SS was not saved by pci_save_aspm_l1ss_state() before reset.

So, if the PCI device has a parent, make pci_save_aspm_l1ss_state() save the parent's L1SS configuration, too. This is symmetric on pci_restore_aspm_l1ss_state().

---
v9:
- Drop the v8 fix about drivers/pci/pcie/aspm.c. Use this in VMD instead.

v10:
- Drop the v9 fix about drivers/pci/controller/vmd.c
- Fix in PCIe ASPM to make it symmetric between pci_save_aspm_l1ss_state() and pci_restore_aspm_l1ss_state()

v11:
- Introduce __pci_save_aspm_l1ss_state as a resusable helper function which is same as the original pci_configure_aspm_l1ss
- Make pci_save_aspm_l1ss_state invoke __pci_save_aspm_l1ss_state for both child and parent devices
- Smooth the commit message

 drivers/pci/pcie/aspm.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

index bd0a8a05647e..17cdf372f7e0 100644
@@ -79,7 +79,7 @@ void pci_configure_aspm_l1ss(struct pci_dev *pdev)
 			ERR_PTR(rc));
 }
 
-void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
+static void __pci_save_aspm_l1ss_state(struct pci_dev *pdev)
 {
 	struct pci_cap_saved_state *save_state;
 	u16 l1ss = pdev->l1ss;

@@ -101,6 +101,24 @@ void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
 	pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL1, cap++);
 }
 
+void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
+{
+	struct pci_dev *parent;
+
+	__pci_save_aspm_l1ss_state(pdev);
+
+	/*
+	 * To be symmetric on pci_restore_aspm_l1ss_state(), save parent's L1
+	 * substate configuration, if the parent has not saved state.
+	 */
+	if (!pdev->bus || !pdev->bus->self)
+		return;
+
+	parent = pdev->bus->self;
+	if (!parent->state_saved)
+		__pci_save_aspm_l1ss_state(parent);
+}
+
 void pci_restore_aspm_l1ss_state(struct pci_dev *pdev)
 {
 	struct pci_cap_saved_state *pl_save_state, *cl_save_state;

2.46.2

This is still misleading because "only one NVMe device" is not the reason why the parent's state is not saved.

Again, please join these sentences.

This tag should appear before signed-off-by.

 i.