Re: [PATCH v5 1/2] ACPI: utils: Add api to read _SUB from ACPI

Rafael J. Wysocki
2022-07-05T16:00:50Z

On Thu, Jun 30, 2022 at 5:01 PM Stefan Binding
<sbinding@opensource.cirrus.com> wrote:
>
> Add a wrapper function to read the _SUB string from ACPI.
>
> Signed-off-by: Stefan Binding <sbinding@opensource.cirrus.com>
> ---
> drivers/acpi/utils.c | 38 ++++++++++++++++++++++++++++++++++++++
> include/linux/acpi.h | 6 ++++++
> 2 files changed, 44 insertions(+)
>
> diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
> index 3a9773a09e19..394954f4b6ef 100644
> --- a/drivers/acpi/utils.c
> +++ b/drivers/acpi/utils.c
> @@ -291,6 +291,44 @@ int acpi_get_local_address(acpi_handle handle, u32 *addr)
> }
> EXPORT_SYMBOL(acpi_get_local_address);
>
> +#define ACPI_MAX_SUB_BUF_SIZE 9
> +
> +const char *acpi_get_subsystem_id(acpi_handle handle)
> +{
> + struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
> + union acpi_object *obj;
> + acpi_status status;
> + const char *sub;
> +
> + status = acpi_evaluate_object(handle, METHOD_NAME__SUB, NULL, &buffer);
> + if (ACPI_FAILURE(status)) {
> + acpi_handle_debug(handle, "Reading ACPI _SUB failed: %#x\n", status);
> + return ERR_PTR(-ENODATA);
> + }
> +
> + obj = buffer.pointer;
> + if (obj->type == ACPI_TYPE_STRING) {
> + if (strlen(obj->string.pointer) < ACPI_MAX_SUB_BUF_SIZE &&
> + strlen(obj->string.pointer) > 0) {
> + sub = kstrdup(obj->string.pointer, GFP_KERNEL);
> + if (!sub)
> + sub = ERR_PTR(-ENOMEM);

The error codes below are somewhat questionable.

> + } else {
> + acpi_handle_err(handle, "ACPI _SUB Length %zu is Invalid\n",
> + strlen(obj->string.pointer));
> + sub = ERR_PTR(-EINVAL);

This is as good as failure, so why not use -ENODATA here?

> + }
> + } else {
> + acpi_handle_warn(handle, "Warning ACPI _SUB did not return a string\n");
> + sub = ERR_PTR(-EINVAL);

Likewise.

> + }
> +
> + acpi_os_free(buffer.pointer);
> +
> + return sub;
> +}
> +EXPORT_SYMBOL_GPL(acpi_get_subsystem_id);
> +
> acpi_status
> acpi_evaluate_reference(acpi_handle handle,
> acpi_string pathname,
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 7b96a8bff6d2..7651198ad6f5 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -762,6 +762,7 @@ static inline u64 acpi_arch_get_root_pointer(void)
> #endif
>
> int acpi_get_local_address(acpi_handle handle, u32 *addr);
> +const char *acpi_get_subsystem_id(acpi_handle handle);
>
> #else /* !CONFIG_ACPI */
>
> @@ -1023,6 +1024,11 @@ static inline int acpi_get_local_address(acpi_handle handle, u32 *addr)
> return -ENODEV;
> }
>
> +static inline const char *acpi_get_subsystem_id(acpi_handle handle)
> +{
> + return ERR_PTR(-ENODEV);
> +}
> +
> static inline int acpi_register_wakeup_handler(int wake_irq,
> bool (*wakeup)(void *context), void *context)
> {
> --
> 2.25.1
>