This patch series adds support for exposing CSU registers through a
sysfs interface. The implementation uses dynamic discovery via the
PM_QUERY_DATA firmware API to determine available registers at
runtime, making the interface flexible and maintainable without
requiring kernel changes when firmware capabilities evolve.

Background:

The ZynqMP platform has several CSU registers that are useful for
system configuration and debugging. Previously, accessing these
registers required direct memory access or custom tools. This series
provides a standardized sysfs interface that leverages existing
firmware APIs for secure access.

Key Features:

- Dynamic register discovery using PM_QUERY_DATA API
  * PM_QID_GET_NODE_COUNT: Query number of available registers
  * PM_QID_GET_NODE_NAME: Query register names by index
- Automatic sysfs attribute creation under csu_registers/ group
- Read operations via existing IOCTL_READ_REG firmware API
- Write operations via existing IOCTL_MASK_WRITE_REG firmware API
- Firmware-enforced access control for read-only registers

Currently Supported Registers:

- multiboot (CSU_MULTI_BOOT): Boot mode configuration
- idcode (CSU_IDCODE): Device identification (read-only)
- pcap-status (CSU_PCAP_STATUS): PCAP status (read-only)

The sysfs interface is available at:
  /sys/devices/platform/firmware:zynqmp-firmware/csu_registers/

Usage Examples:

Reading a register:
  # cat /sys/devices/platform/firmware:zynqmp-firmware/csu_registers/idcode

Writing a register (mask and value in hex):
  # echo "0xFFFFFFFF 0x0" > /sys/devices/platform/firmware:zynqmp-firmware/csu_registers/multiboot


Testing:

- Verified register read operations return correct values
- Verified write operations update registers correctly
- Verified read-only registers reject write attempts
- Verified dynamic discovery works with different firmware versions

Changes in v2:
Patch #1
- Update date

Patch #2:
- Removed unused csu_reg_count field from struct zynqmp_csu_data and
  its kernel-doc entry.
- Added explicit devm_kfree() on the csu_regs and attrs allocation
  failure paths, plus on devm_device_add_group() failure — keeps the
  footprint minimal when CSU is optional.
- Expanded the 0644 sysfs-mode inline comment into a block comment
  explaining the firmware-enforced access-control limitation.Also,
  update the commit message accordingly.
- Added zynqmp_pm_is_function_supported check for PM_QID_GET_NODE_NAME
  ID to mirror the PM_QID_GET_NODE_COUNT verification.

Ronak Jain (2):
  Documentation: ABI: add sysfs interface for ZynqMP CSU registers
  firmware: zynqmp: Add dynamic CSU register discovery and sysfs
    interface

 .../ABI/stable/sysfs-driver-firmware-zynqmp   |  33 +++
 MAINTAINERS                                   |  10 +
 drivers/firmware/xilinx/Makefile              |   2 +-
 drivers/firmware/xilinx/zynqmp-csu-reg.c      | 258 ++++++++++++++++++
 drivers/firmware/xilinx/zynqmp-csu-reg.h      |  18 ++
 drivers/firmware/xilinx/zynqmp.c              |   6 +
 include/linux/firmware/xlnx-zynqmp.h          |   4 +-
 7 files changed, 329 insertions(+), 2 deletions(-)
 create mode 100644 drivers/firmware/xilinx/zynqmp-csu-reg.c
 create mode 100644 drivers/firmware/xilinx/zynqmp-csu-reg.h

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2.34.1