Re: [PATCH v5] drm/vkms: Add support to 1D gamma LUT

[Maira Canal <mairacanal@xxxxxxxxxx>]

Hi Arthur,

On 7/8/23 22:38, Arthur Grillo wrote:
> Support a 1D gamma LUT with interpolation for each color channel on the
> VKMS driver. Add a check for the LUT length by creating
> vkms_atomic_check().
>
> Enable VKMS to run the test igt@kms_plane@pixel-format.
>
> Tested with:
> igt@kms_color@gamma
> igt@kms_color@legacy-gamma
> igt@kms_color@invalid-gamma-lut-sizes
>
> v2:
>      - Add interpolation between the values of the LUT (Simon Ser)
>
> v3:
>      - s/ratio/delta (Pekka)
>      - s/color_channel/channel_value (Pekka)
>      - s/lut_area/lut_channel
>      - Store the `drm_color_lut`, `lut_length`, and
>        `channel_value2index_ratio` inside a struct called `vkms_lut`
>        (Pekka)
>      - Pre-compute some constants values used through the LUT procedure
>        (Pekka)
>      - Change the switch statement to a cast to __u16* (Pekka)
>      - Make the apply_lut_to_channel_value return the computation result
>        (Pekka)
>
> v4:
>      - Add a comment explaining that `enum lut_area` depends on the
>        layout of `struct drm_color_lut` (Pekka)
>      - Remove unused variable (kernel test robot)
>
> v5:
>      - Mention that this will make it possible to run the test
>        igt@kms_plane@pixel-format (Maíra)
>      - s/had/has (Maíra)
>
> Signed-off-by: Arthur Grillo <arthurgrillo@xxxxxxxxxx>
> Acked-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>
> Reviewed-by: Maíra Canal <mairacanal@xxxxxxxxxx>

Applied to drm-misc/drm-misc-next. Thanks for your contribution to VKMS!

Best Regards,
- Maíra

> ---
> Maíra asked me to run a benchmark on some IGT tests:
>
> Each test ran 100 times. The result with 'X' are tests that were not able to
> run because of the absence of gamma LUT.
>
> +--------------------------------------------------+-----------+-----------------+---------------+
> | Test                                             |  No LUT   | Unoptimized LUT | Optimized LUT |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_rotation@primary-rotation-180            | 174.298s  |    181.130s     |   178.800s    |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_plane@pixel-format                       |    X      |    1420.453s    |   1218.229s   |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_plane@pixel-format-source-clamping       |    X      |    704.236s     |   612.318s    |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_plane@plane-position-covered             | 12.535s   |    12.864s      |   12.025s     |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_plane@plane-position-hole                | 11.752s   |    12.873s      |   11.202s     |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_plane@plane-position-hole-dpms           | 15.188s   |    15.238s      |   15.652s     |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_plane@plane-panning-top-left             | 10.797s   |    11.873s      |   11.041s     |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_plane@plane-bottom-right                 | 10.764s   |    11.613s      |   10.053s     |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_plane@plane-panning-bottom-right-suspend | 2011.344s |    2009.410s    |   2011.496s   |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_cursor_crc@cursor-onscreen-512x5112      | 359.209s  |    337.830s     |   308.168s    |
> + -------------------------------------------------+-----------+-----------------+---------------+
> | igt@kms_color@gamma                              |    X      |    137.702s     |   118.139s    |
> + -------------------------------------------------+-----------+-----------------+---------------+
>
> ---
>   drivers/gpu/drm/vkms/vkms_composer.c | 86 ++++++++++++++++++++++++++++
>   drivers/gpu/drm/vkms/vkms_crtc.c     |  3 +
>   drivers/gpu/drm/vkms/vkms_drv.c      | 20 ++++++-
>   drivers/gpu/drm/vkms/vkms_drv.h      |  9 +++
>   4 files changed, 117 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index 906d3df40cdb..e3a79dcd2e38 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -6,6 +6,7 @@
>   #include <drm/drm_atomic_helper.h>
>   #include <drm/drm_blend.h>
>   #include <drm/drm_fourcc.h>
> +#include <drm/drm_fixed.h>
>   #include <drm/drm_gem_framebuffer_helper.h>
>   #include <drm/drm_vblank.h>
>   #include <linux/minmax.h>
> @@ -89,6 +90,73 @@ static void fill_background(const struct pixel_argb_u16 *background_color,
>   		output_buffer->pixels[i] = *background_color;
>   }
>   
> +// lerp(a, b, t) = a + (b - a) * t
> +static u16 lerp_u16(u16 a, u16 b, s64 t)
> +{
> +	s64 a_fp = drm_int2fixp(a);
> +	s64 b_fp = drm_int2fixp(b);
> +
> +	s64 delta = drm_fixp_mul(b_fp - a_fp,  t);
> +
> +	return drm_fixp2int(a_fp + delta);
> +}
> +
> +static s64 get_lut_index(const struct vkms_color_lut *lut, u16 channel_value)
> +{
> +	s64 color_channel_fp = drm_int2fixp(channel_value);
> +
> +	return drm_fixp_mul(color_channel_fp, lut->channel_value2index_ratio);
> +}
> +
> +/*
> + * This enum is related to the positions of the variables inside
> + * `struct drm_color_lut`, so the order of both needs to be the same.
> + */
> +enum lut_channel {
> +	LUT_RED = 0,
> +	LUT_GREEN,
> +	LUT_BLUE,
> +	LUT_RESERVED
> +};
> +
> +static u16 apply_lut_to_channel_value(const struct vkms_color_lut *lut, u16 channel_value,
> +				      enum lut_channel channel)
> +{
> +	s64 lut_index = get_lut_index(lut, channel_value);
> +
> +	/*
> +	 * This checks if `struct drm_color_lut` has any gap added by the compiler
> +	 * between the struct fields.
> +	 */
> +	static_assert(sizeof(struct drm_color_lut) == sizeof(__u16) * 4);
> +
> +	u16 *floor_lut_value = (__u16 *)&lut->base[drm_fixp2int(lut_index)];
> +	u16 *ceil_lut_value = (__u16 *)&lut->base[drm_fixp2int_ceil(lut_index)];
> +
> +	u16 floor_channel_value = floor_lut_value[channel];
> +	u16 ceil_channel_value = ceil_lut_value[channel];
> +
> +	return lerp_u16(floor_channel_value, ceil_channel_value,
> +			lut_index & DRM_FIXED_DECIMAL_MASK);
> +}
> +
> +static void apply_lut(const struct vkms_crtc_state *crtc_state, struct line_buffer *output_buffer)
> +{
> +	if (!crtc_state->gamma_lut.base)
> +		return;
> +
> +	if (!crtc_state->gamma_lut.lut_length)
> +		return;
> +
> +	for (size_t x = 0; x < output_buffer->n_pixels; x++) {
> +		struct pixel_argb_u16 *pixel = &output_buffer->pixels[x];
> +
> +		pixel->r = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->r, LUT_RED);
> +		pixel->g = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->g, LUT_GREEN);
> +		pixel->b = apply_lut_to_channel_value(&crtc_state->gamma_lut, pixel->b, LUT_BLUE);
> +	}
> +}
> +
>   /**
>    * @wb_frame_info: The writeback frame buffer metadata
>    * @crtc_state: The crtc state
> @@ -128,6 +196,8 @@ static void blend(struct vkms_writeback_job *wb,
>   					    output_buffer);
>   		}
>   
> +		apply_lut(crtc_state, output_buffer);
> +
>   		*crc32 = crc32_le(*crc32, (void *)output_buffer->pixels, row_size);
>   
>   		if (wb)
> @@ -242,6 +312,22 @@ void vkms_composer_worker(struct work_struct *work)
>   	crtc_state->frame_start = 0;
>   	crtc_state->frame_end = 0;
>   	crtc_state->crc_pending = false;
> +
> +	if (crtc->state->gamma_lut) {
> +		s64 max_lut_index_fp;
> +		s64 u16_max_fp = drm_int2fixp(0xffff);
> +
> +		crtc_state->gamma_lut.base = (struct drm_color_lut *)crtc->state->gamma_lut->data;
> +		crtc_state->gamma_lut.lut_length =
> +			crtc->state->gamma_lut->length / sizeof(struct drm_color_lut);
> +		max_lut_index_fp = drm_int2fixp(crtc_state->gamma_lut.lut_length  - 1);
> +		crtc_state->gamma_lut.channel_value2index_ratio = drm_fixp_div(max_lut_index_fp,
> +									       u16_max_fp);
> +
> +	} else {
> +		crtc_state->gamma_lut.base = NULL;
> +	}
> +
>   	spin_unlock_irq(&out->composer_lock);
>   
>   	/*
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> index 515f6772b866..61e500b8c9da 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -290,6 +290,9 @@ int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
>   
>   	drm_crtc_helper_add(crtc, &vkms_crtc_helper_funcs);
>   
> +	drm_mode_crtc_set_gamma_size(crtc, VKMS_LUT_SIZE);
> +	drm_crtc_enable_color_mgmt(crtc, 0, false, VKMS_LUT_SIZE);
> +
>   	spin_lock_init(&vkms_out->lock);
>   	spin_lock_init(&vkms_out->composer_lock);
>   
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> index e3c9c9571c8d..dd0af086e7fa 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.c
> +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> @@ -120,9 +120,27 @@ static const struct drm_driver vkms_driver = {
>   	.minor			= DRIVER_MINOR,
>   };
>   
> +static int vkms_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
> +{
> +	struct drm_crtc *crtc;
> +	struct drm_crtc_state *new_crtc_state;
> +	int i;
> +
> +	for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
> +		if (!new_crtc_state->gamma_lut || !new_crtc_state->color_mgmt_changed)
> +			continue;
> +
> +		if (new_crtc_state->gamma_lut->length / sizeof(struct drm_color_lut *)
> +		    > VKMS_LUT_SIZE)
> +			return -EINVAL;
> +	}
> +
> +	return drm_atomic_helper_check(dev, state);
> +}
> +
>   static const struct drm_mode_config_funcs vkms_mode_funcs = {
>   	.fb_create = drm_gem_fb_create,
> -	.atomic_check = drm_atomic_helper_check,
> +	.atomic_check = vkms_atomic_check,
>   	.atomic_commit = drm_atomic_helper_commit,
>   };
>   
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 5f1a0a44a78c..f16b5d7b81ef 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -23,6 +23,8 @@
>   
>   #define NUM_OVERLAY_PLANES 8
>   
> +#define VKMS_LUT_SIZE 256
> +
>   struct vkms_frame_info {
>   	struct drm_framebuffer *fb;
>   	struct drm_rect src, dst;
> @@ -65,6 +67,12 @@ struct vkms_plane {
>   	struct drm_plane base;
>   };
>   
> +struct vkms_color_lut {
> +	struct drm_color_lut *base;
> +	size_t lut_length;
> +	s64 channel_value2index_ratio;
> +};
> +
>   /**
>    * vkms_crtc_state - Driver specific CRTC state
>    * @base: base CRTC state
> @@ -80,6 +88,7 @@ struct vkms_crtc_state {
>   	/* stack of active planes for crc computation, should be in z order */
>   	struct vkms_plane_state **active_planes;
>   	struct vkms_writeback_job *active_writeback;
> +	struct vkms_color_lut gamma_lut;
>   
>   	/* below four are protected by vkms_output.composer_lock */
>   	bool crc_pending;