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)
v3:
- Drop the LUT size check again since
drm_atomic_replace_property_blob_from_id() already covers this for
us. (Alexandru Gheorghe)
Cc: Uma Shankar <uma.shankar@xxxxxxxxx>
Cc: Swati Sharma <swati2.sharma@xxxxxxxxx>
Cc: Brian Starkey <Brian.Starkey@xxxxxxx>
Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
Reviewed-by(v1): Brian Starkey <brian.starkey@xxxxxxx>
Reviewed-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@xxxxxxx>
Reviewed-By: Uma Shankar <uma.shankar@xxxxxxxxx>
---
drivers/gpu/drm/drm_color_mgmt.c | 54 ++++++++++++++++++++++++++++++++++++++++
include/drm/drm_color_mgmt.h | 5 ++++
2 files changed, 59 insertions(+)
diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index 07dcf47daafe..684afcace58f 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -462,3 +462,57 @@ 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 hardware requirements. Drivers pass a bitmask indicating which of
+ * the following tests should 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 || !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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