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

[Shankar, Uma]

>-----Original Message-----
>From: Roper, Matthew D
>Sent: Friday, December 14, 2018 3:25 AM
>To: dri-devel at lists.freedesktop.org; intel-gfx at lists.freedesktop.org
>Cc: Roper, Matthew D <matthew.d.roper at intel.com>; Shankar, Uma
><uma.shankar at intel.com>; Sharma, Swati2 <swati2.sharma at intel.com>; Brian
>Starkey <Brian.Starkey at arm.com>
>Subject: [PATCH v2 1/2] drm: Add color management LUT validation helper (v2)
>
>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)

Looks ok to me.
Reviewed-By: Uma Shankar <uma.shankar at intel.com>

>Cc: Uma Shankar <uma.shankar at intel.com>
>Cc: Swati Sharma <swati2.sharma at intel.com>
>Cc: Brian Starkey <Brian.Starkey at arm.com>
>Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
>Reviewed-by(v1): Brian Starkey <brian.starkey at 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