[PATCH 1/2] drm: add legacy support for using degamma for gamma

[Tomi Valkeinen]

We currently have drm_atomic_helper_legacy_gamma_set() helper which can
be used to handle legacy gamma-set ioctl.
drm_atomic_helper_legacy_gamma_set() sets GAMMA_LUT, and clears
CTM and DEGAMMA_LUT. This works fine on HW where we have either:

degamma -> ctm -> gamma -> out

or

ctm -> gamma -> out

However, if the HW has gamma table before ctm, the atomic property
should be DEGAMMA_LUT, and thus we have:

degamma -> ctm -> out

This is fine for userspace which sets gamma table using the properties,
as the userspace can check for the existence of gamma & degamma, but the
legacy gamma-set ioctl does not work.

This patch fixes the issue by changing
drm_atomic_helper_legacy_gamma_set() so that GAMMA_LUT will be used if
it exists, and DEGAMMA_LUT will be used as a fallback.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
---
 drivers/gpu/drm/drm_atomic_helper.c | 18 +++++++++++++++---
 drivers/gpu/drm/drm_color_mgmt.c    |  4 ++++
 include/drm/drm_crtc.h              |  3 +++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index ba1507036f26..fe59c8ea42a9 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -3512,6 +3512,10 @@ EXPORT_SYMBOL(drm_atomic_helper_page_flip_target);
  * that support color management through the DEGAMMA_LUT/GAMMA_LUT
  * properties. See drm_crtc_enable_color_mgmt() and the containing chapter for
  * how the atomic color management and gamma tables work.
+ *
+ * This function uses the GAMMA_LUT or DEGAMMA_LUT property for the gamma table.
+ * GAMMA_LUT property is used if it exists, and DEGAMMA_LUT property is used as
+ * a fallback.
  */
 int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
 				       u16 *red, u16 *green, u16 *blue,
@@ -3525,6 +3529,12 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
 	struct drm_color_lut *blob_data;
 	int i, ret = 0;
 	bool replaced;
+	bool use_degamma;
+
+	if (!crtc->has_gamma_prop && !crtc->has_degamma_prop)
+		return -ENODEV;
+
+	use_degamma = !crtc->has_gamma_prop;
 
 	state = drm_atomic_state_alloc(crtc->dev);
 	if (!state)
@@ -3554,10 +3564,12 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
 		goto fail;
 	}
 
-	/* Reset DEGAMMA_LUT and CTM properties. */
-	replaced  = drm_property_replace_blob(&crtc_state->degamma_lut, NULL);
+	/* Set GAMMA/DEGAMMA_LUT and reset DEGAMMA/GAMMA_LUT and CTM */
+	replaced  = drm_property_replace_blob(&crtc_state->degamma_lut,
+					      use_degamma ? blob : NULL);
 	replaced |= drm_property_replace_blob(&crtc_state->ctm, NULL);
-	replaced |= drm_property_replace_blob(&crtc_state->gamma_lut, blob);
+	replaced |= drm_property_replace_blob(&crtc_state->gamma_lut,
+					      use_degamma ? NULL : blob);
 	crtc_state->color_mgmt_changed |= replaced;
 
 	ret = drm_atomic_commit(state);
diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index 3bcabc2f6e0e..956e59d5f6a7 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -176,6 +176,8 @@ void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,
 					   degamma_lut_size);
 	}
 
+	crtc->has_degamma_prop = !!degamma_lut_size;
+
 	if (has_ctm)
 		drm_object_attach_property(&crtc->base,
 					   config->ctm_property, 0);
@@ -187,6 +189,8 @@ void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,
 					   config->gamma_lut_size_property,
 					   gamma_lut_size);
 	}
+
+	crtc->has_gamma_prop = !!gamma_lut_size;
 }
 EXPORT_SYMBOL(drm_crtc_enable_color_mgmt);
 
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index ba839e5e357d..9e1f06047e3d 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1084,6 +1084,9 @@ struct drm_crtc {
 	 */
 	uint16_t *gamma_store;
 
+	bool has_gamma_prop;
+	bool has_degamma_prop;
+
 	/** @helper_private: mid-layer private data */
 	const struct drm_crtc_helper_funcs *helper_private;
 
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