[PATCH v6 1/3] PCI: vmd: Set PCI devices to D0 before enable PCI PM's L1 substates

Jian-Hong Pan
2024-06-24T08:15:41Z

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=0ns
L1SubCtl2: T_PwrOn=10us

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".

Link: https://bugzilla.kernel.org/show_bug.cgi?id=218394
Signed-off-by: Jian-Hong Pan <jhp@endlessos.org>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
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:
- The same

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

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index 87b7856f375a..5309afbe31f9 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -751,11 +751,9 @@ 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
@@ -763,7 +761,7 @@ 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
@@ -775,6 +773,13 @@ 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;
}

--
2.45.2