On Tue, 26 Apr 2022, Jouni Högander <jouni.hogander@xxxxxxxxx> wrote:
> Split luminance min/max calculation using static hdr metadata from
> drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c:update_connector_ext_caps
> into drm/drm_edid.c.
IMO all of this should be computed at EDID parsing time once and stored
in the metadata. Maybe in drm_parse_hdr_metadata_block().
Over time we've added a bunch of functions to do this type of stuff, and
all drivers call them at slightly different times and different ways,
and it just grows complicated.
(Also, I think basically everything that comes out of the EDID or
DisplayID should be stored in connector->display_info instead of being
spread around like we currently do. But that's for another patch series,
another time.)
BR,
Jani.
>
> Cc: Rodrigo Siqueira <Rodrigo.Siqueira@xxxxxxx>
> Cc: Harry Wentland <harry.wentland@xxxxxxx>
> Cc: Lyude Paul <lyude@xxxxxxxxxx>
> Cc: Mika Kahola <mika.kahola@xxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Signed-off-by: Jouni Högander <jouni.hogander@xxxxxxxxx>
> ---
> drivers/gpu/drm/drm_edid.c | 55 ++++++++++++++++++++++++++++++++++++++
> include/drm/drm_edid.h | 4 +++
> 2 files changed, 59 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 7a8482b75071..1cb886debbbe 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -4005,6 +4005,61 @@ drm_display_mode_from_cea_vic(struct drm_device *dev,
> }
> EXPORT_SYMBOL(drm_display_mode_from_cea_vic);
>
> +/**
> + * drm_luminance_range_from_static_hdr_metadata() - luminance range from static hdr
> + * metadata
> + * @connector: connector we're calculating for
> + * @min: Calculated min value
> + * @max: Calculated max value
> + *
> + * Calculates backlight min and max as described in CTA-861-G
> + *
> + * Returns: True when calculation succeeds.
> + */
> +bool
> +drm_luminance_range_from_static_hdr_metadata(struct drm_connector *connector,
> + u32 *min, u32 *max)
> +{
> + struct hdr_sink_metadata *hdr_metadata = &connector->hdr_sink_metadata;
> + static const u8 pre_computed_values[] = {
> + 50, 51, 52, 53, 55, 56, 57, 58, 59, 61, 62, 63, 65, 66, 68, 69,
> + 71, 72, 74, 75, 77, 79, 81, 82, 84, 86, 88, 90, 92, 94, 96, 98};
> + u32 min_cll, max_cll, q, r;
> +
> + if (!(hdr_metadata->hdmi_type1.metadata_type &
> + BIT(HDMI_STATIC_METADATA_TYPE1)))
> + return false;
> +
> + max_cll = hdr_metadata->hdmi_type1.max_cll;
> + min_cll = hdr_metadata->hdmi_type1.min_cll;
> +
> + /* From the specification (CTA-861-G), for calculating the maximum
> + * luminance we need to use:
> + * Luminance = 50*2**(CV/32)
> + * Where CV is a one-byte value.
> + * For calculating this expression we may need float point precision;
> + * to avoid this complexity level, we take advantage that CV is divided
> + * by a constant. From the Euclids division algorithm, we know that CV
> + * can be written as: CV = 32*q + r. Next, we replace CV in the
> + * Luminance expression and get 50*(2**q)*(2**(r/32)), hence we just
> + * need to pre-compute the value of r/32. For pre-computing the values
> + * We just used the following Ruby line:
> + * (0...32).each {|cv| puts (50*2**(cv/32.0)).round}
> + * The results of the above expressions can be verified at
> + * pre_computed_values.
> + */
> + q = max_cll >> 5;
> + r = max_cll % 32;
> + *max = (1 << q) * pre_computed_values[r];
> +
> + /* min luminance: maxLum * (CV/255)^2 / 100 */
> + q = DIV_ROUND_CLOSEST(min_cll, 255);
> + *min = *max * DIV_ROUND_CLOSEST((q * q), 100);
> +
> + return true;
> +}
> +EXPORT_SYMBOL(drm_luminance_range_from_static_hdr_metadata);
> +
> static int
> do_cea_modes(struct drm_connector *connector, const u8 *db, u8 len)
> {
> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
> index c3204a58fb09..63e441c84d72 100644
> --- a/include/drm/drm_edid.h
> +++ b/include/drm/drm_edid.h
> @@ -406,6 +406,10 @@ drm_hdmi_avi_infoframe_quant_range(struct hdmi_avi_infoframe *frame,
> const struct drm_display_mode *mode,
> enum hdmi_quantization_range rgb_quant_range);
>
> +bool
> +drm_luminance_range_from_static_hdr_metadata(struct drm_connector *connector,
> + u32 *min, u32 *max);
> +
> /**
> * drm_eld_mnl - Get ELD monitor name length in bytes.
> * @eld: pointer to an eld memory structure with mnl set
--
Jani Nikula, Intel Open Source Graphics Center
