PCI: Add PTM debugfs support

Hi,

This series adds debugfs support to expose the PTM context available in the
capable PCIe controllers. Support for enabling PTM in the requester/responder is
already available in drivers/pci/pcie.c and this series expands that file to
add debugfs support for the PTM context info.

The controller drivers are expected to call pcie_ptm_create_debugfs() with
'pcie_ptm_ops' callbacks populated to create the debugfs entries and call
pcie_ptm_destroy_debugfs() to destroy them.

Patch 1 adds the necessary code in the drivers/pci/pcie.c to expose PTM
context over debugfs and patch 2 adds PTM support in the DWC drivers (host and
endpoint). Finally, patch 3 masks the PTM_UPDATING interrupt in the pcie-qcom-ep
driver to avoid processing the interrupt for each PTM context update.

Testing
=======

This series is tested on Qcom SA8775p Ride Mx platform where one SA8775p acts as
RC and another as EP with following instructions:

RC
--

$ echo 1 > /sys/kernel/debug/pcie_ptm_1c10000.pcie/context_valid

EP
--

$ echo auto > /sys/kernel/debug/pcie_ptm_1c10000.pcie-ep/context_update

$ cat /sys/kernel/debug/pcie_ptm_1c10000.pcie-ep/local_clock
159612570424

$ cat /sys/kernel/debug/pcie_ptm_1c10000.pcie-ep/master_clock
159609466232

$ cat /sys/kernel/debug/pcie_ptm_1c10000.pcie-ep/t1
159609466112

$ cat /sys/kernel/debug/pcie_ptm_1c10000.pcie-ep/t4
159609466518

NOTE: To make use of the PTM feature, the host PCIe client driver has to call
'pci_enable_ptm()' API during probe. This series was tested with enabling PTM in
the MHI host driver with a local change (which will be upstreamed later).
Technically, PTM could also be enabled in the pci_endpoint_test driver, but I
didn't add the change as I'm not sure we'd want to add random PCIe features in
the test driver without corresponding code in pci-epf-test driver.

Changes in v3:
- Switched to debugfs interface based on comments from Bjorn
- Added locking for context read/writes
- Rebased on top of v6.15-rc1
- Link to v2: https://lore.kernel.org/r/20250324-pcie-ptm-v2-0-c7d8c364...

Changes in v2:

* Dropped the VSEC changes that got merged
* Moved the PTM sysfs code from drivers/pci/controller/dwc to
  drivers/pci/pcie/ptm.c to make it generic so that other controller drivers could
  also benefit from it.
* Rebased on top of pci/controller/dwc

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
Manivannan Sadhasivam (4):
      PCI: Add debugfs support for exposing PTM context
      PCI: dwc: Pass DWC PCIe mode to dwc_pcie_debugfs_init()
      PCI: dwc: Add debugfs support for PTM context
      PCI: qcom-ep: Mask PTM_UPDATING interrupt

 Documentation/ABI/testing/debugfs-pcie-ptm         |  70 +++++
 MAINTAINERS                                        |   1 +
 .../pci/controller/dwc/pcie-designware-debugfs.c   | 252 ++++++++++++++++-
 drivers/pci/controller/dwc/pcie-designware-ep.c    |   2 +-
 drivers/pci/controller/dwc/pcie-designware-host.c  |   2 +-
 drivers/pci/controller/dwc/pcie-designware.c       |   6 +
 drivers/pci/controller/dwc/pcie-designware.h       |  24 +-
 drivers/pci/controller/dwc/pcie-qcom-ep.c          |   8 +
 drivers/pci/pcie/ptm.c                             | 300 +++++++++++++++++++++
 include/linux/pci.h                                |  45 ++++
 include/linux/pcie-dwc.h                           |   8 +
 11 files changed, 713 insertions(+), 5 deletions(-)
---
base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
change-id: 20250324-pcie-ptm-e75b9b2ffcfb

Best regards,
-- 
Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>