[PATCH v7 1/4] drm: Define histogram structures exposed to user

[Arun R Murthy]

Display Histogram is an array of bins and can be generated in many ways
referred to as modes.
Ex: HSV max(RGB), Wighted RGB etc.

Understanding the histogram data format(Ex: HSV max(RGB))
Histogram is just the pixel count.
For a maximum resolution of 10k (10240 x 4320 = 44236800)
25 bits should be sufficient to represent this along with a buffer of 7
bits(future use) u32 is being considered.
max(RGB) can be 255 i.e 0xFF 8 bit, considering the most significant 5
bits, hence 32 bins.
Below mentioned algorithm illustrates the histogram generation in
hardware.

hist[32] = {0};
for (i = 0; i < resolution; i++) {
	bin = max(RGB[i]);
	bin = bin >> 3;	/* consider the most significant bits */
	hist[bin]++;
}
If the entire image is Red color then max(255,0,0) is 255 so the pixel
count of each pixels will be placed in the last bin. Hence except
hist[31] all other bins will have a value zero.
Generated histogram in this case would be hist[32] = {0,0,....44236800}

Description of the structures, properties defined are documented in the
header file include/uapi/drm/drm_mode.h

Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
---
 include/uapi/drm/drm_mode.h | 59 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index c082810c08a8b234ef2672ecf54fc8c05ddc2bd3..7a7039381142bb5dba269bdaec42c18be34e2d05 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -1355,6 +1355,65 @@ struct drm_mode_closefb {
 	__u32 pad;
 };
 
+/*
+ * Maximum resolution at present 10k, 10240x4320 = 44236800
+ * can be denoted in 25bits. With an additional 7 bits in buffer each bin
+ * can be a u32 value.
+ * Maximum value of max(RGB) is 255, so max 255 bins.
+ * If the most significant 5 bits are considered, then bins = 0xff >> 3
+ * will be 32 bins.
+ * For illustration consider a full RED image of 10k resolution considering all
+ * 8 bits histogram would look like hist[255] = {0,0,....44236800}
+ */
+#define DRM_MODE_HISTOGRAM_HSV_MAX_RGB			(1 << 0)
+
+/**
+ * struct drm_histogram_caps
+ *
+ * @histogram_mode: histogram generation modes, defined in the above macros
+ * @bins_count: number of bins for a chosen histogram mode. For illustration
+ *		refer the above defined histogram mode.
+ */
+struct drm_histogram_caps {
+	u8 histogram_mode;
+	u32 bins_count;
+};
+
+/**
+ * struct drm_histogram_config
+ *
+ * @enable: flag to enable/disable histogram
+ * @hist_mode: histogram mode(HSV max(RGB), RGB, LUMA etc)
+ * @reserved1: Reserved for future use
+ * @reserved2: Reserved for future use
+ * @reserved3: Reserved for future use
+ * @reserved4: Reserved for future use
+ */
+struct drm_histogram_config {
+	bool enable;
+	u8 hist_mode;
+	u32 reserved1;
+	u32 reserved2;
+	u32 reserved3;
+	u32 reserved4;
+};
+
+/**
+ * struct drm_histogram
+ *
+ * @config: histogram configuration data pointed by struct drm_histogram_config
+ * @data_ptr: pointer to the array of histogram.
+ *	      Histogram is an array of bins. Data format for each bin depends
+ *	      on the histogram mode. Refer to the above histogram modes for
+ *	      more information.
+ * @nr_elements: number of bins in the histogram.
+ */
+struct drm_histogram {
+	struct drm_histogram_config config;
+	__u64 data_ptr;
+	__u32 nr_elements;
+};
+
 #if defined(__cplusplus)
 }
 #endif

-- 
2.25.1