[PATCH v2 1/2] drm: Add color management LUT validation helper (v2)

[Matt Roper <matthew.d.roper@intel.com>]

Some hardware may place additional restrictions on the gamma/degamma
curves described by our LUT properties.  E.g., that a gamma curve never
decreases or that the red/green/blue channels of a LUT's entries must be
equal.  Let's add a helper function that drivers can use to test that a
userspace-provided LUT is valid and doesn't violate hardware
requirements.

v2:
 - Combine into a single helper that just takes a bitmask of the tests
   to apply.  (Brian Starkey)
 - Add additional check (always performed) that LUT property blob size
   is always a multiple of the LUT entry size.  (stolen from ARM driver)

Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Swati Sharma <swati2.sharma@intel.com>
Cc: Brian Starkey <Brian.Starkey@arm.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by(v1): Brian Starkey <brian.starkey@arm.com>
---
 drivers/gpu/drm/drm_color_mgmt.c | 64 ++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_color_mgmt.h     |  5 ++++
 2 files changed, 69 insertions(+)

diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index 07dcf47daafe..5c2a2d228412 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -462,3 +462,67 @@ int drm_plane_create_color_properties(struct drm_plane *plane,
 	return 0;
 }
 EXPORT_SYMBOL(drm_plane_create_color_properties);
+
+/**
+ * drm_color_lut_check - check validity of lookup table
+ * @lut: property blob containing LUT to check
+ * @tests: bitmask of tests to run
+ *
+ * Helper to check whether a userspace-provided lookup table is valid and
+ * satisfies additional hardware requirements.  All table sizes should be a
+ * multiple of sizeof(struct drm_color_lut).  Drivers pass a bitmask indicating
+ * which of the following additional tests should also be performed:
+ *
+ * "DRM_COLOR_LUT_EQUAL_CHANNELS":
+ *     Checks whether the entries of a LUT all have equal values for the red,
+ *     green, and blue channels.  Intended for hardware that only accepts a
+ *     single value per LUT entry and assumes that value applies to all three
+ *     color components.
+ *
+ * "DRM_COLOR_LUT_INCREASING":
+ *     Checks whether the entries of a LUT are always flat or increasing
+ *     (never decreasing).
+ *
+ * Returns 0 on success, -EINVAL on failure.
+ */
+int drm_color_lut_check(struct drm_property_blob *lut,
+			 uint32_t tests)
+{
+	struct drm_color_lut *entry;
+	int i;
+
+	if (!lut)
+		return 0;
+
+	if (lut->length % sizeof(struct drm_color_lut)) {
+		DRM_DEBUG_KMS("LUT size (%lu) is not a multiple of LUT entry size (%lu)\n",
+			      lut->length, sizeof(struct drm_color_lut));
+		return -EINVAL;
+	}
+
+	if (!tests)
+		return 0;
+
+	entry = lut->data;
+	for (i = 0; i < drm_color_lut_size(lut); i++) {
+		if (tests & DRM_COLOR_LUT_EQUAL_CHANNELS) {
+			if (entry[i].red != entry[i].blue ||
+			    entry[i].red != entry[i].green) {
+				DRM_DEBUG_KMS("All LUT entries must have equal r/g/b\n");
+				return -EINVAL;
+			}
+		}
+
+		if (i > 0 && tests & DRM_COLOR_LUT_INCREASING) {
+			if (entry[i].red < entry[i - 1].red ||
+			    entry[i].green < entry[i - 1].green ||
+			    entry[i].blue < entry[i - 1].blue) {
+				DRM_DEBUG_KMS("LUT entries must never decrease.\n");
+				return -EINVAL;
+			}
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_color_lut_check);
diff --git a/include/drm/drm_color_mgmt.h b/include/drm/drm_color_mgmt.h
index 90ef9996d9a4..7de16f70bcc3 100644
--- a/include/drm/drm_color_mgmt.h
+++ b/include/drm/drm_color_mgmt.h
@@ -69,4 +69,9 @@ int drm_plane_create_color_properties(struct drm_plane *plane,
 				      u32 supported_ranges,
 				      enum drm_color_encoding default_encoding,
 				      enum drm_color_range default_range);
+
+#define DRM_COLOR_LUT_EQUAL_CHANNELS BIT(0)
+#define DRM_COLOR_LUT_INCREASING     BIT(1)
+int drm_color_lut_check(struct drm_property_blob *lut,
+			uint32_t tests);
 #endif
-- 
2.14.4

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