[RFC v5 1/8] drm: Add Enhanced Gamma LUT precision structure

[Uma Shankar]

Existing LUT precision structure is having only 16 bit
precision. This is not enough for upcoming enhanced hardwares
and advance usecases like HDR processing. Hence added a new
structure with 32 bit precision values. Also added the code,
for extracting the same from values passed from userspace.

v4: Rebase

v5: Relocated the helper function to drm_color_mgmt.c. Declared
the same in a header file (Alexandru Gheorghe)

Signed-off-by: Uma Shankar <uma.shankar at intel.com>
Reviewed-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe at arm.com>
---
 drivers/gpu/drm/drm_color_mgmt.c | 19 +++++++++++++++++++
 include/drm/drm_color_mgmt.h     |  1 +
 include/uapi/drm/drm_mode.h      | 15 +++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index b97e2de..1bdcc1a 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -128,6 +128,25 @@ uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision)
 }
 EXPORT_SYMBOL(drm_color_lut_extract);
 
+/*
+ * Added to accommodate enhanced LUT precision.
+ * Max LUT precision is 32 bits.
+ */
+uint32_t drm_color_lut_extract_ext(uint32_t user_input, uint32_t bit_precision)
+{
+	uint32_t val = user_input;
+	uint32_t max = 0xffffffff >> (32 - bit_precision);
+
+	/* Round only if we're not using full precision. */
+	if (bit_precision < 32) {
+		val += 1UL << (32 - bit_precision - 1);
+		val >>= 32 - bit_precision;
+	}
+
+	return clamp_val(val, 0, max);
+}
+EXPORT_SYMBOL(drm_color_lut_extract_ext);
+
 /**
  * drm_crtc_enable_color_mgmt - enable color management properties
  * @crtc: DRM CRTC
diff --git a/include/drm/drm_color_mgmt.h b/include/drm/drm_color_mgmt.h
index 44f04233..78b5a37 100644
--- a/include/drm/drm_color_mgmt.h
+++ b/include/drm/drm_color_mgmt.h
@@ -29,6 +29,7 @@
 struct drm_plane;
 
 uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision);
+uint32_t drm_color_lut_extract_ext(uint32_t user_input, uint32_t bit_precision);
 
 void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,
 				uint degamma_lut_size,
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index 8d67243..874407b 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -629,6 +629,21 @@ struct drm_color_lut {
 	__u16 reserved;
 };
 
+/*
+ * Creating 32 bit palette entries for better data
+ * precision. This will be required for HDR and
+ * similar color processing usecases.
+ */
+struct drm_color_lut_ext {
+	/*
+	 * Data is U0.32 fixed point format.
+	 */
+	__u32 red;
+	__u32 green;
+	__u32 blue;
+	__u32 reserved;
+};
+
 #define DRM_MODE_PAGE_FLIP_EVENT 0x01
 #define DRM_MODE_PAGE_FLIP_ASYNC 0x02
 #define DRM_MODE_PAGE_FLIP_TARGET_ABSOLUTE 0x4
-- 
1.9.1