[PATCH v1 1/2] ACPI: utils: Add api to read _SUB from ACPI

[Rafael J. Wysocki]

On Wed, Jun 22, 2022 at 3:08 PM Stefan Binding
<sbinding at opensource.cirrus.com> wrote:
>
> Add a wrapper function to read the _SUB string from ACPI.
>
> Signed-off-by: Stefan Binding <sbinding at opensource.cirrus.com>
> ---
>  drivers/acpi/utils.c | 26 ++++++++++++++++++++++++++
>  include/linux/acpi.h |  8 ++++++++
>  2 files changed, 34 insertions(+)
>
> diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
> index 3a9773a09e19..5d1bdb79e372 100644
> --- a/drivers/acpi/utils.c
> +++ b/drivers/acpi/utils.c
> @@ -291,6 +291,32 @@ int acpi_get_local_address(acpi_handle handle, u32 *addr)
>  }
>  EXPORT_SYMBOL(acpi_get_local_address);
>
> +int acpi_get_sub(acpi_handle handle, char *sub, size_t size)

I'd call it acpi_get_subsystem_id().

> +{
> +       struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
> +       union acpi_object *obj;
> +       acpi_status status;
> +       int ret;
> +
> +       status = acpi_evaluate_object(handle, METHOD_NAME__SUB, NULL, &buffer);
> +       if (!ACPI_SUCCESS(status)) {

Typically, ACPI_FAILURE() is used in checks like this.

> +               acpi_handle_debug(handle, "Reading ACPI _SUB failed: %#x\n", status);

It would be enough to say "_SUB evaluation failed".

> +               return -ENOENT;

Why not use -ENODATA here?

> +       }
> +
> +       obj = buffer.pointer;
> +       if (obj->type == ACPI_TYPE_STRING) {
> +               ret = strscpy(sub, obj->string.pointer, size);

It may be simpler to allocate the memory here so that callers don't
have to worry about it.

Also, this is expected to be a proper device ID, not just a string, so
maybe some validation checks could be made here?

> +       } else {
> +               acpi_handle_warn(handle, "Warning ACPI _SUB did not return a string\n");
> +               ret = -EINVAL;
> +       }
> +       acpi_os_free(buffer.pointer);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(acpi_get_sub);
> +
>  acpi_status
>  acpi_evaluate_reference(acpi_handle handle,
>                         acpi_string pathname,
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 4f82a5bc6d98..9bf18adf5920 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -21,6 +21,8 @@
>  #endif
>  #include <acpi/acpi.h>
>
> +#define ACPI_MAX_SUB_BUF_SIZE  9
> +
>  #ifdef CONFIG_ACPI
>
>  #include <linux/list.h>
> @@ -762,6 +764,7 @@ static inline u64 acpi_arch_get_root_pointer(void)
>  #endif
>
>  int acpi_get_local_address(acpi_handle handle, u32 *addr);
> +int acpi_get_sub(acpi_handle handle, char *sub, size_t size);
>
>  #else  /* !CONFIG_ACPI */
>
> @@ -1023,6 +1026,11 @@ static inline int acpi_get_local_address(acpi_handle handle, u32 *addr)
>         return -ENODEV;
>  }
>
> +static int acpi_get_sub(acpi_handle handle, char *sub, size_t size)
> +{
> +       return -ENODEV;
> +}
> +
>  static inline int acpi_register_wakeup_handler(int wake_irq,
>         bool (*wakeup)(void *context), void *context)
>  {
> --