[PATCH v5 0/3] PCI: qcom: Program T_POWER_ON value for L1.2 exit timing

[Krishna Chaitanya Chundru]

The T_POWER_ON indicates the time (in μs) that a Port requires the port
on the opposite side of Link to wait in L1.2.Exit after sampling CLKREQ#
asserted before actively driving the interface. This value is used by
the ASPM driver to compute the LTR_L1.2_THRESHOLD.

Currently, qcom root port exposes T_POWER_ON value of zero in the L1SS
capability registers, leading to incorrect LTR_L1.2_THRESHOLD calculations,
which can result in improper L1.2 exit behavior and can trigger AER's.

In this series, qcom controller drivers read the devicetree property
"t-power-on" which got merged recently[1], and use that value to over
write default/wrong value.

To convert T_POWER_ON in to T_POWER_ON_SCALE & T_POWER_ON_VALUE created
a pcie_encode_t_power_on() helper in aspm.c and also created
dw_pcie_program_t_power_on() helper for other drivers to use these
helpers.

Link [1]: https://lore.kernel.org/all/20260205093346.667898-1-krishna.chundru@xxxxxxxxxxxxxxxx/

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>
---
Changes in v5:
- Initialize *scale & *value to zero incase of ASPM is disabled pointed
  by sashiko.
- Use dwc readl & writel API's instead of direct readl & writel pointed
  by sashiko
- couple of nits (Mani).
- Link to v4: https://lore.kernel.org/r/20260404-t_power_on_fux-v4-0-2891391177f4@xxxxxxxxxxxxxxxx

Changes in v4:
- calculate maxv from PCI_L1SS_CTL2_T_PWR_ON_VALUE to PCI_L1SS_CAP_P_PWR_ON_VALUE (Mani).
- added a todo to move the reading the devicetree from qcom driver to
  dwc once multi root port parsing support is added (Mani).
- Link to v3: https://lore.kernel.org/r/20260311-t_power_on_fux-v3-0-9b1f1d09c6f3@xxxxxxxxxxxxxxxx

Changes in v3:
- move pcie_encode_t_power_on() include/linux/pci.h to
  drivers/pci/pci.h (Bjorn).
- couple of changes in commit text and variable name like t_power_on (Bjorn).
- remove return 0 from qcom_pcie_configure_ports (Bjorn).
- used FIELD_MODIFY instead of FIELD_PREP (Bjorn).
- Link to v2: https://lore.kernel.org/r/20260223-t_power_on_fux-v2-0-20c921262709@xxxxxxxxxxxxxxxx

Changes in v2:
- Instead of hard coding the values in the driver, created a devicetree
  property "t-power-on" to program it (Bjorn & Mani).
- Link to v1: https://lore.kernel.org/r/20251104-t_power_on_fux-v1-1-eb5916e47fd7@xxxxxxxxxxxxxxxx

To: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
To: Jingoo Han <jingoohan1@xxxxxxxxx>
To: Manivannan Sadhasivam <mani@xxxxxxxxxx>
To: Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx>
To: Krzysztof Wilczyński <kwilczynski@xxxxxxxxxx>
To: Rob Herring <robh@xxxxxxxxxx>
Cc: linux-pci@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-arm-msm@xxxxxxxxxxxxxxx

---
Krishna Chaitanya Chundru (3):
      PCI/ASPM: Add helper to encode L1SS T_POWER_ON fields
      PCI: dwc: Add helper to Program T_POWER_ON
      PCI: qcom: Program T_POWER_ON

 drivers/pci/controller/dwc/pcie-designware.c | 28 +++++++++++++++++++
 drivers/pci/controller/dwc/pcie-designware.h |  1 +
 drivers/pci/controller/dwc/pcie-qcom.c       | 14 ++++++++++
 drivers/pci/pci.h                            |  6 +++++
 drivers/pci/pcie/aspm.c                      | 40 ++++++++++++++++++++++++++++
 5 files changed, 89 insertions(+)
---
base-commit: 3b3bea6d4b9c162f9e555905d96b8c1da67ecd5b
change-id: 20251104-t_power_on_fux-70dc68377941

Best regards,
--  
Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>