Re: [PATCH v4 2/2] spmi: core: Add generic DebugFS interface for bus inspection

[Abel Vesa]

On 26-10-30 10:29:47, vamshi gajjela wrote:
> From: Vamshi Gajjela <vamshigajjela@xxxxxxxxxx>
> 
> Introduce a generic, controller-agnostic DebugFS interface in the SPMI
> core under /sys/kernel/debug/spmi/spmi-<nr>/:
> - name: Displays the controller parent device name and OF node.
> - xfer: Transactional interface supporting register reads, writes,
>   and directed command opcodes with automatic opcode selection.
> 
> Because raw writes and commands to PMICs can damage hardware and bypass
> client drivers and their regmap caches, write ('w') and command ('c')
> operations are disabled by default behind SPMI_ALLOW_WRITE_DEBUGFS. When
> enabled, they restrict access to root (mode 0600) and mark the kernel
> tainted with TAINT_USER.
> 
> Detailed interface syntax and parameters are documented in
> Documentation/ABI/testing/debugfs-spmi.
> 
> Co-developed-by: Jim Wylder <jwylder@xxxxxxxxxx>
> Signed-off-by: Jim Wylder <jwylder@xxxxxxxxxx>
> Signed-off-by: Vamshi Gajjela <vamshigajjela@xxxxxxxxxx>
> ---
>  Documentation/ABI/testing/debugfs-spmi |  68 +++++
>  MAINTAINERS                            |   1 +
>  drivers/spmi/Makefile                  |   1 +
>  drivers/spmi/spmi-core.c               |  20 +-
>  drivers/spmi/spmi-debugfs.c            | 341 +++++++++++++++++++++++++
>  drivers/spmi/spmi-internal.h           |  28 ++
>  include/linux/spmi.h                   |   6 +
>  7 files changed, 459 insertions(+), 6 deletions(-)
>  create mode 100644 Documentation/ABI/testing/debugfs-spmi
>  create mode 100644 drivers/spmi/spmi-debugfs.c
>  create mode 100644 drivers/spmi/spmi-internal.h
> 
> diff --git a/Documentation/ABI/testing/debugfs-spmi b/Documentation/ABI/testing/debugfs-spmi
> new file mode 100644
> index 000000000000..6a0bff9027a4
> --- /dev/null
> +++ b/Documentation/ABI/testing/debugfs-spmi
> @@ -0,0 +1,68 @@
> +What:		/sys/kernel/debug/spmi/spmi-<nr>/name
> +Date:		October 2026
> +KernelVersion:	7.4
> +Contact:	vamshi gajjela <vamshigajjela@xxxxxxxxxx>
> +Description:
> +		Displays the SPMI controller parent device name and
> +		associated Device Tree node.
> +Users:		Debugging, hardware diagnostics
> +
> +What:		/sys/kernel/debug/spmi/spmi-<nr>/xfer
> +Date:		October 2026
> +KernelVersion:	7.4

This patch won't make it into 7.4, so you can say 7.5 here.

> +Contact:	vamshi gajjela <vamshigajjela@xxxxxxxxxx>
> +Description:
> +		Transactional interface for raw SPMI bus operations:
> +
> +		- Register Read:
> +		    exec 3<> xfer && echo "r <sid> <addr> [len]" >&3 && cat <&3
> +		  Reads 1 to 16 bytes starting at <addr> from slave <sid>.
> +		  The optional [len] parameter defaults to 1 byte.
> +		  Output is formatted as:
> +		    0x<addr>: <byte0> <byte1> ...
> +		  Each open file descriptor maintains an independent response
> +		  buffer. Reading from the same open file descriptor consumes
> +		  the response; subsequent reads return EOF (0 bytes) until a
> +		  new read command is written.
> +

[...]

> +
> +void spmi_controller_debugfs_init(struct spmi_controller *ctrl)
> +{
> +	struct dentry *dentry;
> +	char name[32];
> +
> +	if (IS_ERR_OR_NULL(spmi_debugfs_root))
> +		return;
> +
> +	snprintf(name, sizeof(name), "spmi-%u", ctrl->nr);
> +	dentry = debugfs_create_dir(name, spmi_debugfs_root);
> +	if (IS_ERR_OR_NULL(dentry))
> +		return;

No need to check debugfs return values, please drop these.

Also, the dir name is the same as dev_name(&ctrl->dev), so please use that.