[PATCH v2 3/3] drm/i915/bios: abstract child device expected size

[Chauhan, Shekhar]

On 2/26/2024 23:28, Jani Nikula wrote:
> Add a function to return the expected child device size. Flip the if
> ladder around and use the same versions as in documentation to make it
> easier to verify. Return an error for unknown versions. No functional
> changes.
>
> v2: Move BUILD_BUG_ON() next to the expected sizes
>
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_bios.c | 40 ++++++++++++++---------
>   1 file changed, 24 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index c0f41bd1f946..343726de9aa7 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -2699,27 +2699,35 @@ static void parse_ddi_ports(struct drm_i915_private *i915)
>   		print_ddi_port(devdata);
>   }
>   
> +static int child_device_expected_size(u16 version)
> +{
> +	BUILD_BUG_ON(sizeof(struct child_device_config) < 40);
> +
> +	if (version > 256)
> +		return -ENOENT;
> +	else if (version >= 256)
Correct me if I'm wrong, but isn't version >= 256, a bit cryptic after 
the first check?
Would it be wise to make it version > 256, return -ENOENT and if version 
== 256, return 40?
> +		return 40;
> +	else if (version >= 216)
> +		return 39;
> +	else if (version >= 196)
> +		return 38;
> +	else if (version >= 195)
> +		return 37;
> +	else if (version >= 111)
> +		return LEGACY_CHILD_DEVICE_CONFIG_SIZE;
> +	else if (version >= 106)
> +		return 27;
> +	else
> +		return 22;
> +}
> +
>   static bool child_device_size_valid(struct drm_i915_private *i915, int size)
>   {
>   	int expected_size;
>   
> -	if (i915->display.vbt.version < 106) {
> -		expected_size = 22;
> -	} else if (i915->display.vbt.version < 111) {
> -		expected_size = 27;
> -	} else if (i915->display.vbt.version < 195) {
> -		expected_size = LEGACY_CHILD_DEVICE_CONFIG_SIZE;
> -	} else if (i915->display.vbt.version == 195) {
> -		expected_size = 37;
> -	} else if (i915->display.vbt.version <= 215) {
> -		expected_size = 38;
> -	} else if (i915->display.vbt.version <= 255) {
> -		expected_size = 39;
> -	} else if (i915->display.vbt.version <= 256) {
> -		expected_size = 40;
> -	} else {
> +	expected_size = child_device_expected_size(i915->display.vbt.version);
> +	if (expected_size < 0) {
>   		expected_size = sizeof(struct child_device_config);
> -		BUILD_BUG_ON(sizeof(struct child_device_config) < 40);
>   		drm_dbg(&i915->drm,
>   			"Expected child device config size for VBT version %u not known; assuming %d\n",
>   			i915->display.vbt.version, expected_size);

-- 
-shekhar