[PATCH v3 0/4] PCI: dwc: Add ECAM support with iATU configuration

Krishna Chaitanya Chundru
2025-01-21T09:02:45Z

The current implementation requires iATU for every configuration
space access which increases latency & cpu utilization.

Designware databook 5.20a, section 3.10.10.3 says about CFG Shift Feature,
which shifts/maps the BDF (bits [31:16] of the third header DWORD, which
would be matched against the Base and Limit addresses) of the incoming
CfgRd0/CfgWr0 down to bits[27:12]of the translated address.

Configuring iATU in config shift mode enables ECAM feature to access the
config space, which avoids iATU configuration for every config access.

Add cfg_shft_mode into struct dw_pcie_ob_atu_cfg to enable config shift mode.

As DBI comes under config space, this avoids remapping of DBI space
separately. Instead, it uses the mapped config space address returned from
ECAM initialization. Change the order of dw_pcie_get_resources() execution
to acheive this.

Enable the ECAM feature if the config space size is equal to size required
to represent number of buses in the bus range property.

The ELBI registers falls after the DBI space, PARF_SLV_DBI_ELBI register
gives us the offset from which ELBI starts. so use this offset and cfg
win to map these regions instead of doing the ioremap again.

On root bus, we have only the root port. Any access other than that
should not go out of the link and should return all F's. Since the iATU
is configured for the buses which starts after root bus, block the
transactions starting from function 1 of the root bus to the end of
the root bus (i.e from dbi_base + 4kb to dbi_base + 1MB) from going
outside the link through ECAM blocker through PARF registers.

Increase the configuration size to 256MB as required by the ECAM feature
and also move config space, DBI, iATU to upper space and use lower space
entirely for BAR region.

Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
---
Changes in v3:
- if bus range is less than 2 return with out configuring iATU for next
bus & update the logic of ecam_supported() as suggested ( Konrad)
- updated commit text and update S-o-b (Bjorn Andresson)
- Link to v2: https://lore.kernel.org/r/20241224-enable_ecam-v2-0-43daef68a901@oss.qualcomm.com

changes in v2:
- rename enable_ecam to ecam_mode as suggested by mani.
- refactor changes as suggested by bjorn
- remove ecam_init() function op as we have removed ELBI virtual address
update from the ecam_init and moved to host init as we need the clocks
to be enabled to read the ELBI offset from the PARF registers.
- Update comments and commit message as suggested by bjorn.
- Allocate host bridge in the DWC glue drivers as suggested by bjorn
- move qcom_pcie_ecam_supported to dwc as suggested by mani.
Link to v1: https://lore.kernel.org/r/linux-devicetree/20241117-ecam-v1-1-6059faf38d07@quicinc.com/T/

---
Krishna Chaitanya Chundru (4):
arm64: dts: qcom: sc7280: Increase config size to 256MB for ECAM feature
PCI: dwc: Add ECAM support with iATU configuration
PCI: dwc: Reduce DT reads by allocating host bridge via DWC glue driver
PCI: qcom: Enable ECAM feature

arch/arm64/boot/dts/qcom/sc7280.dtsi | 12 +-
drivers/pci/controller/dwc/Kconfig | 1 +
drivers/pci/controller/dwc/pcie-designware-host.c | 148 ++++++++++++++++++----
drivers/pci/controller/dwc/pcie-designware.c | 2 +-
drivers/pci/controller/dwc/pcie-designware.h | 11 ++
drivers/pci/controller/dwc/pcie-qcom.c | 81 +++++++++++-
6 files changed, 221 insertions(+), 34 deletions(-)
---
base-commit: e989da8ac2a4999cf6edfaf55880909577d438cd
change-id: 20241211-enable_ecam-f9f94b7269b9

Best regards,
--
Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>