[PATCH v2 0/4] HDR aux backlight range calculation

[PATCH v2 0/4] HDR aux backlight range calculation

[Jouni Högander]

This patch set splits out static hdr metadata backlight range parsing
from gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c into gpu/drm/drm-edid.c
as a new function. This new function is then used during edid parsing
when HDR static metadata block parsing.

Calculated values are stored in a new struct drm_luminance_range
introduced into display_info. Amdgpu_dm.c and intel_dp_aux_backlight.c
are using this new data.

v2: Calculate the range during edid parsing and store into display_info

Cc: Roman Li <roman.li@amd.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>

Jouni Högander (4):
  drm/display: Add drm_luminance_range_info
  drm: New function to get luminance range based on static hdr metadata
  drm/amdgpu_dm: Rely on split out luminance calculation function
  drm/i915: Use luminance range calculated during edid parsing

 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 35 ++-----------
 drivers/gpu/drm/drm_edid.c                    | 50 ++++++++++++++++++-
 .../drm/i915/display/intel_dp_aux_backlight.c | 17 +++++--
 include/drm/drm_connector.h                   | 21 ++++++++
 4 files changed, 88 insertions(+), 35 deletions(-)

-- 
2.25.1

[PATCH v2 1/4] drm/display: Add drm_luminance_range_info

[Jouni Högander]

Add new data structure to store luminance range calculated using
data from EDID's static hdr metadata block. Add this new struct
as a part of drm_display_info struct.

Cc: Roman Li <roman.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
---
 include/drm/drm_connector.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 3ac4bf87f257..7d8eeac6cc68 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -322,6 +322,22 @@ struct drm_monitor_range_info {
 	u8 max_vfreq;
 };
 
+/**
+ * struct drm_luminance_range_info - Panel's luminance range for
+ * &drm_display_info. Calculated using data in EDID
+ *
+ * This struct is used to store a luminance range supported by panel
+ * as calculated using data from EDID's static hdr metadata.
+ *
+ * @min_luminance: This is the min supported luminance value
+ *
+ * @max_luminance: This is the max supported luminance value
+ */
+struct drm_luminance_range_info {
+	u32 min_luminance;
+	u32 max_luminance;
+};
+
 /**
  * enum drm_privacy_screen_status - privacy screen status
  *
@@ -623,6 +639,11 @@ struct drm_display_info {
 	 */
 	struct drm_monitor_range_info monitor_range;
 
+	/**
+	 * @luminance_range: Luminance range supported by panel
+	 */
+	struct drm_luminance_range_info luminance_range;
+
 	/**
 	 * @mso_stream_count: eDP Multi-SST Operation (MSO) stream count from
 	 * the DisplayID VESA vendor block. 0 for conventional Single-Stream
-- 
2.25.1

[PATCH v2 2/4] drm: New function to get luminance range based on static hdr metadata

[Jouni Högander]

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 and use it during edid parsing. Calculated range is
stored into connector->display_info->luminance_range.

v2: Calculate range during edid parsing

Cc: Roman Li <roman.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
---
 drivers/gpu/drm/drm_edid.c | 50 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 2bdaf1e34a9d..3b367100290f 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -5014,6 +5014,49 @@ static void fixup_detailed_cea_mode_clock(struct drm_display_mode *mode)
 	mode->clock = clock;
 }
 
+static void drm_calculate_luminance_range(struct drm_connector *connector)
+{
+	struct hdr_static_metadata *hdr_metadata = &connector->hdr_sink_metadata.hdmi_type1;
+	struct drm_luminance_range_info *luminance_range =
+		&connector->display_info.luminance_range;
+	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 max_avg, min_cll, max, min, q, r;
+
+	if (!(hdr_metadata->metadata_type & BIT(HDMI_STATIC_METADATA_TYPE1)))
+		return;
+
+	max_avg = hdr_metadata->max_fall;
+	min_cll = hdr_metadata->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_avg >> 5;
+	r = max_avg % 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);
+
+	luminance_range->min_luminance = min;
+	luminance_range->max_luminance = max;
+}
+
 static uint8_t eotf_supported(const u8 *edid_ext)
 {
 	return edid_ext[2] &
@@ -5045,8 +5088,12 @@ drm_parse_hdr_metadata_block(struct drm_connector *connector, const u8 *db)
 		connector->hdr_sink_metadata.hdmi_type1.max_cll = db[4];
 	if (len >= 5)
 		connector->hdr_sink_metadata.hdmi_type1.max_fall = db[5];
-	if (len >= 6)
+	if (len >= 6) {
 		connector->hdr_sink_metadata.hdmi_type1.min_cll = db[6];
+
+		/* Calculate only when all values are available */
+		drm_calculate_luminance_range(connector);
+	}
 }
 
 static void
@@ -5951,6 +5998,7 @@ drm_reset_display_info(struct drm_connector *connector)
 
 	info->non_desktop = 0;
 	memset(&info->monitor_range, 0, sizeof(info->monitor_range));
+	memset(&info->luminance_range, 0, sizeof(info->luminance_range));
 
 	info->mso_stream_count = 0;
 	info->mso_pixel_overlap = 0;
-- 
2.25.1

[PATCH v2 3/4] drm/amdgpu_dm: Rely on split out luminance calculation function

[Jouni Högander]

Luminance range calculation was split out into drm_edid.c and is now
part of edid parsing. Rely on values calculated during edid parsing and
use these for caps->aux_max_input_signal and caps->aux_min_input_signal.

v2: Use values calculated during edid parsing

Cc: Roman Li <roman.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 35 +++----------------
 1 file changed, 4 insertions(+), 31 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 428bb041f92c..896a6b5eb2ed 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -2813,15 +2813,12 @@ static struct drm_mode_config_helper_funcs amdgpu_dm_mode_config_helperfuncs = {
 
 static void update_connector_ext_caps(struct amdgpu_dm_connector *aconnector)
 {
-	u32 max_avg, min_cll, max, min, q, r;
 	struct amdgpu_dm_backlight_caps *caps;
 	struct amdgpu_display_manager *dm;
 	struct drm_connector *conn_base;
 	struct amdgpu_device *adev;
 	struct dc_link *link = NULL;
-	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};
+	struct drm_luminance_range_info *luminance_range;
 	int i;
 
 	if (!aconnector || !aconnector->dc_link)
@@ -2843,8 +2840,6 @@ static void update_connector_ext_caps(struct amdgpu_dm_connector *aconnector)
 	caps = &dm->backlight_caps[i];
 	caps->ext_caps = &aconnector->dc_link->dpcd_sink_ext_caps;
 	caps->aux_support = false;
-	max_avg = conn_base->hdr_sink_metadata.hdmi_type1.max_fall;
-	min_cll = conn_base->hdr_sink_metadata.hdmi_type1.min_cll;
 
 	if (caps->ext_caps->bits.oled == 1 /*||
 	    caps->ext_caps->bits.sdr_aux_backlight_control == 1 ||
@@ -2856,31 +2851,9 @@ static void update_connector_ext_caps(struct amdgpu_dm_connector *aconnector)
 	else if (amdgpu_backlight == 1)
 		caps->aux_support = true;
 
-	/* 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_avg >> 5;
-	r = max_avg % 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);
-
-	caps->aux_max_input_signal = max;
-	caps->aux_min_input_signal = min;
+	luminance_range = &conn_base->display_info.luminance_range;
+	caps->aux_min_input_signal = luminance_range->min_luminance;
+	caps->aux_max_input_signal = luminance_range->max_luminance;
 }
 
 void amdgpu_dm_update_connector_after_detect(
-- 
2.25.1

[PATCH v2 4/4] drm/i915: Use luminance range calculated during edid parsing

[Jouni Högander]

Instead of using fixed 0 - 512 range use luminance range calculated
as a part of edid parsing. As a backup fall back to static 0 - 512.

v2: Use values calculated during edid parsing

Cc: Lyude Paul <lyude@redhat.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
---
 .../drm/i915/display/intel_dp_aux_backlight.c   | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
index c92d5bb2326a..b2666bd67701 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
@@ -276,8 +276,11 @@ intel_dp_aux_hdr_disable_backlight(const struct drm_connector_state *conn_state,
 static int
 intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pipe)
 {
-	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct drm_connector *conn_base = &connector->base;
+	struct drm_i915_private *i915 = to_i915(conn_base->dev);
 	struct intel_panel *panel = &connector->panel;
+	struct drm_luminance_range_info *luminance_range =
+		&conn_base->display_info.luminance_range;
 	int ret;
 
 	if (panel->backlight.edp.intel.sdr_uses_aux) {
@@ -293,8 +296,16 @@ intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pi
 		}
 	}
 
-	panel->backlight.max = 512;
-	panel->backlight.min = 0;
+	if (!luminance_range->max_luminance) {
+		panel->backlight.max = 512;
+		panel->backlight.min = 0;
+	} else {
+		panel->backlight.max = luminance_range->max_luminance;
+		panel->backlight.min = luminance_range->min_luminance;
+	}
+
+	drm_dbg(&i915->drm, "Using range %d..%d\n", panel->backlight.min, panel->backlight.max);
+
 	panel->backlight.level = intel_dp_aux_hdr_get_backlight(connector, pipe);
 	panel->backlight.enabled = panel->backlight.level != 0;
 
-- 
2.25.1

Re: [PATCH v2 4/4] drm/i915: Use luminance range calculated during edid parsing

[Jani Nikula]

On Mon, 20 Jun 2022, Jouni Högander <jouni.hogander@intel.com> wrote:
> Instead of using fixed 0 - 512 range use luminance range calculated
> as a part of edid parsing. As a backup fall back to static 0 - 512.
>
> v2: Use values calculated during edid parsing
>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Mika Kahola <mika.kahola@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> ---
>  .../drm/i915/display/intel_dp_aux_backlight.c   | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> index c92d5bb2326a..b2666bd67701 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -276,8 +276,11 @@ intel_dp_aux_hdr_disable_backlight(const struct drm_connector_state *conn_state,
>  static int
>  intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pipe)
>  {
> -	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> +	struct drm_connector *conn_base = &connector->base;

Nitpick, we never call this "conn_base". Usually we try to avoid having
drm_connector as local variable altogether, but if you must, please name
it _connector or drm_connector.

> +	struct drm_i915_private *i915 = to_i915(conn_base->dev);
>  	struct intel_panel *panel = &connector->panel;
> +	struct drm_luminance_range_info *luminance_range =
> +		&conn_base->display_info.luminance_range;
>  	int ret;
>  
>  	if (panel->backlight.edp.intel.sdr_uses_aux) {
> @@ -293,8 +296,16 @@ intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pi
>  		}
>  	}
>  
> -	panel->backlight.max = 512;
> -	panel->backlight.min = 0;
> +	if (!luminance_range->max_luminance) {

Nitpick, I kind of dislike these "if (!something) ... else ..."
constructs when you could avoid the negative by switching it around.

> +		panel->backlight.max = 512;
> +		panel->backlight.min = 0;
> +	} else {
> +		panel->backlight.max = luminance_range->max_luminance;
> +		panel->backlight.min = luminance_range->min_luminance;
> +	}
> +
> +	drm_dbg(&i915->drm, "Using range %d..%d\n", panel->backlight.min, panel->backlight.max);

Please use drm_dbg_kms(). Please say *what* range this is. Otherwise,
you have to figure it out from the context and function names.

> +
>  	panel->backlight.level = intel_dp_aux_hdr_get_backlight(connector, pipe);
>  	panel->backlight.enabled = panel->backlight.level != 0;

-- 
Jani Nikula, Intel Open Source Graphics Center

Re: [PATCH v2 1/4] drm/display: Add drm_luminance_range_info

[Jani Nikula]

On Mon, 20 Jun 2022, Jouni Högander <jouni.hogander@intel.com> wrote:
> Add new data structure to store luminance range calculated using
> data from EDID's static hdr metadata block. Add this new struct
> as a part of drm_display_info struct.
>
> Cc: Roman Li <roman.li@amd.com>
> Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Mika Kahola <mika.kahola@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>

LGTM but I think I'd just fold this into the next patch that actually
uses it.

BR,
Jani.

> ---
>  include/drm/drm_connector.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 3ac4bf87f257..7d8eeac6cc68 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -322,6 +322,22 @@ struct drm_monitor_range_info {
>  	u8 max_vfreq;
>  };
>  
> +/**
> + * struct drm_luminance_range_info - Panel's luminance range for
> + * &drm_display_info. Calculated using data in EDID
> + *
> + * This struct is used to store a luminance range supported by panel
> + * as calculated using data from EDID's static hdr metadata.
> + *
> + * @min_luminance: This is the min supported luminance value
> + *
> + * @max_luminance: This is the max supported luminance value
> + */
> +struct drm_luminance_range_info {
> +	u32 min_luminance;
> +	u32 max_luminance;
> +};
> +
>  /**
>   * enum drm_privacy_screen_status - privacy screen status
>   *
> @@ -623,6 +639,11 @@ struct drm_display_info {
>  	 */
>  	struct drm_monitor_range_info monitor_range;
>  
> +	/**
> +	 * @luminance_range: Luminance range supported by panel
> +	 */
> +	struct drm_luminance_range_info luminance_range;
> +
>  	/**
>  	 * @mso_stream_count: eDP Multi-SST Operation (MSO) stream count from
>  	 * the DisplayID VESA vendor block. 0 for conventional Single-Stream

-- 
Jani Nikula, Intel Open Source Graphics Center

Re: [PATCH v2 2/4] drm: New function to get luminance range based on static hdr metadata

[Jani Nikula]

On Mon, 20 Jun 2022, Jouni Högander <jouni.hogander@intel.com> 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 and use it during edid parsing. Calculated range is
> stored into connector->display_info->luminance_range.
>
> v2: Calculate range during edid parsing
>
> Cc: Roman Li <roman.li@amd.com>
> Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Mika Kahola <mika.kahola@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> ---
>  drivers/gpu/drm/drm_edid.c | 50 +++++++++++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 2bdaf1e34a9d..3b367100290f 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -5014,6 +5014,49 @@ static void fixup_detailed_cea_mode_clock(struct drm_display_mode *mode)
>  	mode->clock = clock;
>  }
>  
> +static void drm_calculate_luminance_range(struct drm_connector *connector)
> +{
> +	struct hdr_static_metadata *hdr_metadata = &connector->hdr_sink_metadata.hdmi_type1;
> +	struct drm_luminance_range_info *luminance_range =
> +		&connector->display_info.luminance_range;
> +	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};

Nitpick, newline before };

> +	u32 max_avg, min_cll, max, min, q, r;
> +
> +	if (!(hdr_metadata->metadata_type & BIT(HDMI_STATIC_METADATA_TYPE1)))
> +		return;
> +
> +	max_avg = hdr_metadata->max_fall;
> +	min_cll = hdr_metadata->min_cll;
> +
> +	/* From the specification (CTA-861-G), for calculating the maximum

Nitpick, newline after /*.

> +	 * 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_avg >> 5;
> +	r = max_avg % 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);
> +
> +	luminance_range->min_luminance = min;
> +	luminance_range->max_luminance = max;

I'll just trust this; not going to start verifying.

Acked-by: Jani Nikula <jani.nikula@intel.com>

> +}
> +
>  static uint8_t eotf_supported(const u8 *edid_ext)
>  {
>  	return edid_ext[2] &
> @@ -5045,8 +5088,12 @@ drm_parse_hdr_metadata_block(struct drm_connector *connector, const u8 *db)
>  		connector->hdr_sink_metadata.hdmi_type1.max_cll = db[4];
>  	if (len >= 5)
>  		connector->hdr_sink_metadata.hdmi_type1.max_fall = db[5];
> -	if (len >= 6)
> +	if (len >= 6) {
>  		connector->hdr_sink_metadata.hdmi_type1.min_cll = db[6];
> +
> +		/* Calculate only when all values are available */
> +		drm_calculate_luminance_range(connector);
> +	}
>  }
>  
>  static void
> @@ -5951,6 +5998,7 @@ drm_reset_display_info(struct drm_connector *connector)
>  
>  	info->non_desktop = 0;
>  	memset(&info->monitor_range, 0, sizeof(info->monitor_range));
> +	memset(&info->luminance_range, 0, sizeof(info->luminance_range));
>  
>  	info->mso_stream_count = 0;
>  	info->mso_pixel_overlap = 0;

-- 
Jani Nikula, Intel Open Source Graphics Center