Re: [Intel-gfx] [PATCH 2/3] drm: Add Wrapper Functions for ELD SAD Extraction

[Jani Nikula <jani.nikula@intel.com>]

On Mon, 21 Aug 2023, Mitul Golani <mitulkumar.ajitkumar.golani@intel.com> wrote:
> Add wrapper functions to facilitate extracting Short Audio
> Descriptor (SAD) information from EDID-Like Data (ELD) pointers
> with different constness requirements.
>
> 1. `drm_eld_sad`: This function returns a constant `uint8_t`
> pointer and wraps the main extraction function, allowing access
> to SAD information while maintaining const correctness.
>
> 2. `drm_extract_sad_from_eld`: This function returns a mutable
> `uint8_t` pointer and implements the core logic for extracting
> SAD from the provided ELD pointer. It performs version and
> maximum channel checks to ensure proper extraction.
>
> These wrapper functions provide flexibility to the codebase,
> allowing users to access SAD information while adhering to
> const correctness when needed and modifying the pointer when
> required.

I've considered this, and in the end I think it's better to *not* make
it easier for drivers to modify the ELD buffer directly.

To that end, I wrote some helpers to modify the SADs using the existing
struct cea_sad abstraction [1]. Please have a look. It should make your
changes better focus on what you need to do here, instead of getting
distracted with ELD parsing details.

BR,
Jani.


[1] https://patchwork.freedesktop.org/series/123384/


>
> Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
> ---
>  include/drm/drm_edid.h | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
> index 48e93f909ef6..626bc0d542eb 100644
> --- a/include/drm/drm_edid.h
> +++ b/include/drm/drm_edid.h
> @@ -418,11 +418,7 @@ static inline int drm_eld_mnl(const uint8_t *eld)
>  	return (eld[DRM_ELD_CEA_EDID_VER_MNL] & DRM_ELD_MNL_MASK) >> DRM_ELD_MNL_SHIFT;
>  }
>  
> -/**
> - * drm_eld_sad - Get ELD SAD structures.
> - * @eld: pointer to an eld memory structure with sad_count set
> - */
> -static inline const uint8_t *drm_eld_sad(const uint8_t *eld)
> +static uint8_t *drm_extract_sad_from_eld(uint8_t *eld)
>  {
>  	unsigned int ver, mnl;
>  
> @@ -437,6 +433,15 @@ static inline const uint8_t *drm_eld_sad(const uint8_t *eld)
>  	return eld + DRM_ELD_CEA_SAD(mnl, 0);
>  }
>  
> +/**
> + * drm_eld_sad - Get ELD SAD structures.
> + * @eld: pointer to an eld memory structure with sad_count set
> + */
> +static inline const uint8_t *drm_eld_sad(const uint8_t *eld)
> +{
> +	return drm_extract_sad_from_eld((uint8_t *)eld);
> +}
> +
>  /**
>   * drm_eld_sad_count - Get ELD SAD count.
>   * @eld: pointer to an eld memory structure with sad_count set

-- 
Jani Nikula, Intel Open Source Graphics Center