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

[Daniel Vetter <daniel@ffwll.ch>]

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)
> 
> 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).

For internal stuff an enum would be much better (you can still do
bitmasks), that also gives you a nice way to document the enum values
using kerneldoc. With enums you can then document them like a struct,
using inline comments.

This style here we only use for properties, which are real strings (hence
the "", for C constants/defines that looks funny).

Cheers, Daniel

> + *
> + * 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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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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