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.
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
--
2.25.1
