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

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(+)

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
>

On Thu, Jun 30, 2022 at 5:17 PM Stefan Binding
<sbinding@opensource.cirrus.com> wrote:
>
> Add a wrapper function to read the _SUB string from ACPI.

...

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

Three times to evaluate strlen()... Can we do better, please?

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