[PATCH v8 4/4] PCI/ASPM: Fix L1.2 parameters when enable link state

[Jian-Hong Pan <jhp@endlessos.org>]

Currently, when enable link's L1.2 features with __pci_enable_link_state(),
it configs the link directly without ensuring related L1.2 parameters, such
as T_POWER_ON, Common_Mode_Restore_Time, and LTR_L1.2_THRESHOLD have been
programmed.

This leads the link's L1.2 between PCIe Root Port and child device gets
wrong configs when a caller tries to enabled it.

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

10000:e0:06.0 PCI bridge: Intel Corporation 11th Gen Core Processor PCIe Controller (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=45us LTR1.2_Threshold=101376ns
        L1SubCtl2: T_PwrOn=50us

10000:e1:00.0 Non-Volatile memory controller: Sandisk Corp WD Blue SN550 NVMe SSD (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=0ns
        L1SubCtl2: T_PwrOn=10us

According to "PCIe r6.0, sec 5.5.4", before enabling ASPM L1.2 on the PCIe
Root Port and the child NVMe, they should be programmed with the same
LTR1.2_Threshold value. However, they have different values in this case.

Invoke aspm_calc_l12_info() to program the L1.2 parameters properly before
enable L1.2 bits of L1 PM Substates Control Register in
__pci_enable_link_state().

Link: https://bugzilla.kernel.org/show_bug.cgi?id=218394
Signed-off-by: Jian-Hong Pan <jhp@endlessos.org>
---
v2:
- Prepare the PCIe LTR parameters before enable L1 Substates

v3:
- Only enable supported features for the L1 Substates part

v4:
- Focus on fixing L1.2 parameters, instead of re-initializing whole L1SS

v5:
- Fix typo and commit message
- Split introducing aspm_get_l1ss_cap() to "PCI/ASPM: Introduce
  aspm_get_l1ss_cap()"

v6:
- Skipped

v7:
- Pick back and rebase on the new version kernel
- Drop the link state flag check. And, always config link state's timing
  parameters

v8:
- Because pcie_aspm_get_link() might return the link as NULL, move
  getting the link's parent and child devices after check the link is
  not NULL. This avoids NULL memory access.

 drivers/pci/pcie/aspm.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 5db1044c9895..55ff1d26fcea 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -1411,9 +1411,15 @@ EXPORT_SYMBOL(pci_disable_link_state);
 static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
 {
 	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
+	u32 parent_l1ss_cap, child_l1ss_cap;
+	struct pci_dev *parent, *child;
 
 	if (!link)
 		return -EINVAL;
+
+	parent = link->pdev;
+	child = link->downstream;
+
 	/*
 	 * A driver requested that ASPM be enabled on this device, but
 	 * if we don't have permission to manage ASPM (e.g., on ACPI
@@ -1428,6 +1434,15 @@ static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
 	if (!locked)
 		down_read(&pci_bus_sem);
 	mutex_lock(&aspm_lock);
+	/*
+	 * Ensure L1.2 parameters: Common_Mode_Restore_Times, T_POWER_ON and
+	 * LTR_L1.2_THRESHOLD are programmed properly before enable bits for
+	 * L1.2, per PCIe r6.0, sec 5.5.4.
+	 */
+	parent_l1ss_cap = aspm_get_l1ss_cap(parent);
+	child_l1ss_cap = aspm_get_l1ss_cap(child);
+	aspm_calc_l12_info(link, parent_l1ss_cap, child_l1ss_cap);
+
 	link->aspm_default = pci_calc_aspm_enable_mask(state);
 	pcie_config_aspm_link(link, policy_to_aspm_state(link));
 
-- 
2.45.2