Add a DRM plane property "color_mode" for panels that support
3-color (black/white/red) display modes.

The property allows runtime selection between:
  - bw (black/white): R1 format represents black (0) and white (1)
  - 3color: R1 format represents red ink (1) on white background

The property is created on all panels with "black-white" selectable;
panels with red_supported = true also expose the "3-color" option.
The default is set from the panel configuration's default_color_mode
field (typically BW for monochrome panels).

Signed-off-by: Devarsh Thakkar <[email protected]>
---
Changes in v3:
- Reject 3-color mode together with partial refresh in the plane
  atomic_check, as partial refresh does not update the red channel
- Only create the color_mode property on panels with a red plane instead
  of exposing a property with a single possible value
---
 drivers/gpu/drm/solomon/ssd16xx.c | 51 +++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/drivers/gpu/drm/solomon/ssd16xx.c 
b/drivers/gpu/drm/solomon/ssd16xx.c
index f53c67ae7d31..6037717635a4 100644
--- a/drivers/gpu/drm/solomon/ssd16xx.c
+++ b/drivers/gpu/drm/solomon/ssd16xx.c
@@ -399,6 +399,7 @@ struct ssd16xx_device {
        u8  spi_buf[64] ____cacheline_aligned; /* DMA-safe buffer for SPI 
transfers */
 
        struct drm_property *refresh_mode_property;
+       struct drm_property *color_mode_property;
 };
 
 /* Plane state subclass: refresh_mode lives on the plane, not the connector,
@@ -407,6 +408,7 @@ struct ssd16xx_device {
 struct ssd16xx_plane_state {
        struct drm_shadow_plane_state base;
        enum ssd16xx_refresh_mode refresh_mode; /* Pending refresh mode */
+       enum ssd16xx_color_mode color_mode;     /* Pending color mode */
 };
 
 #define to_ssd16xx_plane_state(s) \
@@ -1457,6 +1459,7 @@ static struct drm_plane_state 
*ssd16xx_plane_atomic_create_state(struct drm_plan
 
        __drm_gem_shadow_plane_state_init(plane, &ssd_state->base);
        ssd_state->refresh_mode = device->refresh_mode;
+       ssd_state->color_mode = device->color_mode;
 
        return &ssd_state->base.base;
 }
@@ -1499,6 +1502,10 @@ static int ssd16xx_plane_atomic_get_property(struct 
drm_plane *plane,
                *val = ssd_state->refresh_mode;
                return 0;
        }
+       if (property == device->color_mode_property) {
+               *val = ssd_state->color_mode;
+               return 0;
+       }
        return -EINVAL;
 }
 
@@ -1516,6 +1523,18 @@ static int ssd16xx_plane_atomic_set_property(struct 
drm_plane *plane,
                ssd_state->refresh_mode = val;
                return 0;
        }
+       if (property == device->color_mode_property) {
+               if (val > SSD16XX_COLOR_MODE_3COLOR)
+                       return -EINVAL;
+               if (val == SSD16XX_COLOR_MODE_3COLOR &&
+                   !device->device_cfg->red_supported) {
+                       drm_dbg(&device->drm,
+                               "3-color not supported by this panel\n");
+                       return -EINVAL;
+               }
+               ssd_state->color_mode = val;
+               return 0;
+       }
        return -EINVAL;
 }
 
@@ -1535,11 +1554,20 @@ static int ssd16xx_plane_atomic_check(struct drm_plane 
*plane,
 {
        struct drm_plane_state *new_plane_state =
                drm_atomic_get_new_plane_state(state, plane);
+       struct ssd16xx_plane_state *ssd_state =
+               to_ssd16xx_plane_state(new_plane_state);
        struct drm_crtc_state *crtc_state;
 
        if (!new_plane_state->crtc)
                return 0;
 
+       if (ssd_state->color_mode == SSD16XX_COLOR_MODE_3COLOR &&
+           ssd_state->refresh_mode == SSD16XX_REFRESH_PARTIAL) {
+               drm_dbg_atomic(plane->dev,
+                              "3-color mode does not support partial 
refresh\n");
+               return -EINVAL;
+       }
+
        crtc_state = drm_atomic_get_new_crtc_state(state, 
new_plane_state->crtc);
 
        return drm_atomic_helper_check_plane_state(new_plane_state, crtc_state,
@@ -1608,6 +1636,7 @@ static void ssd16xx_plane_atomic_update(struct drm_plane 
*plane,
        }
 
        device->refresh_mode = new_ssd->refresh_mode;
+       device->color_mode = new_ssd->color_mode;
 
        /*
         * When refresh_mode_init was set, use the specified mode for this first
@@ -1855,6 +1884,11 @@ static const struct drm_prop_enum_list 
ssd16xx_refresh_mode_enum[] = {
        { SSD16XX_REFRESH_FAST,    "fast"    },
 };
 
+static const struct drm_prop_enum_list ssd16xx_color_mode_enum[] = {
+       { SSD16XX_COLOR_MODE_BW,     "black-white" },
+       { SSD16XX_COLOR_MODE_3COLOR, "3-color"     },
+};
+
 static int ssd16xx_plane_create_properties(struct ssd16xx_device *device)
 {
        struct drm_device *drm = &device->drm;
@@ -1869,6 +1903,23 @@ static int ssd16xx_plane_create_properties(struct 
ssd16xx_device *device)
        drm_object_attach_property(plane_obj,
                                   device->refresh_mode_property,
                                   device->refresh_mode);
+
+       /*
+        * Color mode: only meaningful on panels with a physical red plane.
+        * BW-only panels get no property at all rather than a one-value knob.
+        */
+       if (!device->device_cfg->red_supported)
+               return 0;
+
+       device->color_mode_property =
+               drm_property_create_enum(drm, 0, "color_mode",
+                                        ssd16xx_color_mode_enum,
+                                        ARRAY_SIZE(ssd16xx_color_mode_enum));
+       if (!device->color_mode_property)
+               return -ENOMEM;
+       drm_object_attach_property(plane_obj,
+                                  device->color_mode_property,
+                                  device->color_mode);
        return 0;
 }
 
-- 
2.39.1

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