Hi Matt,
On Thu, Dec 13, 2018 at 01:55:25PM -0800, Matt Roper wrote:
> 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)
nit: Technically we're 'Arm' now
>
> 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>
Looks good to me, feel free to drop the (v1) qualifier. Thanks again!
-Brian
> ---
> 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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