Phil-Engljaehringer opened a new pull request, #21079:
URL: https://github.com/apache/nuttx/pull/21079
arch/arm/src/imx9: scmi: Add BBM GPR get and set.
## Summary
* New feature: the i.MX95 BBNSM (battery-backed non-secure module) has
eight
32-bit general purpose registers (GPRs). They keep their value across
resets of any logical machine (LM), as long as the battery-backed power
domain stays powered.
On the i.MX95 the M7 has no direct access to them; the SM owns the BBNSM
and
exposes the GPRs through the SCMI BBM protocol (0x81).
* This adds two request functions to `arch/arm/src/imx9/imx9_scmi.c`:
* `imx9_scmi_bbmgprset(channel, index, value)` -> `BBM_GPR_SET` (0x3)
* `imx9_scmi_bbmgprget(channel, index, *value)` -> `BBM_GPR_GET` (0x4)
They follow the structure of the existing request functions (A2P lock,
buffer init, a2ptx, a2prx, unlock) and the message layout of the imx-sm
reference client (`components/scmi/scmi_bbm.c`).
* `imx9_scmi.h` gets the SCMI status codes `SCMI_ERR_NOT_SUPPORTED` (-1) ..
`SCMI_ERR_PROTOCOL_ERROR` (-10). The request functions return the SM's
SCMI status unchanged, so callers need these to tell, for example,
`SCMI_ERR_DENIED` apart from other failures. These values overlap with
negated errno values; the header says so. A CRC error on the response
returns `-EIO`, which equals `SCMI_ERR_OUT_OF_RANGE`; the doc blocks of
both functions note this.
* The SM configuration must grant the agent access to the GPR
(`GET` or higher to read, `EXCLUSIVE` or higher to write), otherwise the
SM answers `SCMI_ERR_DENIED`.
* Use case: PX4 on the M7 of the MR-NAVQ95B uses one GPR as a word that
survives M7 and Linux resets and that the SM can read too (for example a
reset lockout while the vehicle is armed). That code lives in the PX4
board
support; there is no in-tree caller in NuttX.
## Impact
* Is new feature added? Is existing feature changed? YES, two new imx9 SCMI
request functions and the SCMI status code defines. No existing function
changes.
* Impact on user (will user need to adapt to change)? NO.
* Impact on build (will build process change)? NO.
* Impact on hardware (will arch(s) / board(s) / driver(s) change)? YES,
only
`arch/arm/src/imx9` (SCMI). Built only with `CONFIG_IMX9_SCMI`.
* Impact on documentation (is update required / provided)? NO, the
functions
are documented in `imx9_scmi.h`.
* Impact on security (any sort of implications)? NO, access to the GPRs is
enforced by the System Manager configuration.
* Impact on compatibility (backward/forward/interoperability)? NO.
## Testing
I confirm that changes are verified on local setup and works as intended:
* Build Host(s): Linux 6.17 x86_64, AMD Ryzen AI 9 HX 370,
arm-none-eabi-gcc 14.2.1 20241119.
* Target(s): ARM Cortex-M7, i.MX95 (MR-NAVQ95B).
Runtime tested on hardware (MR-NAVQ95B, SM configuration granting the M7
agent access to GPR7) with a NuttX 12.12 based tree containing the
identical change: a value written with `imx9_scmi_bbmgprset()` is read back
with `imx9_scmi_bbmgprget()`. On current master the commit was build tested
(`mr-navq95b:rpmsg` and `mr-navq95b:nsh`, no warnings).
`./tools/checkpatch.sh -f` on both files and
`./tools/checkpatch.sh -c -u -m -g HEAD~1..HEAD` pass.
AI assistance: the port to master, the commit message and this description
were prepared with Claude Code (claude-opus-5-5), see the `Assisted-by`
tag.
I reviewed the change, tested it on hardware as described above, and signed
it off.
## PR verification Self-Check
* [x] This PR introduces only one functional change.
* [x] I have updated all required description fields above.
* [x] My PR adheres to Contributing
[Guidelines](https://github.com/apache/nuttx/blob/master/CONTRIBUTING.md) and
[Documentation](https://nuttx.apache.org/docs/latest/contributing/index.html)
(git commit title and message, coding standard, etc).
* [ ] My PR is still work in progress (not ready for review).
* [x] My PR is ready for review and can be safely merged into a codebase.
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