[PATCH] drm/stm: ltdc: add clut mode support

[Philippe Cornu]

Add the 8-bit clut mode support at crtc level.
Useful for low memory footprint user interfaces but also for
8-bit old games (including color shifting visual effects).
Tested with fbdev FBIOPUTCMAP & drm DRM_IOCTL_MODE_SETGAMMA
ioctls.

Signed-off-by: Philippe Cornu <philippe.co...@st.com>
---
 drivers/gpu/drm/stm/ltdc.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
index 7be6710..d5c8a42 100644
--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c
@@ -174,6 +174,8 @@
 
 #define LXCFBLNR_CFBLN GENMASK(10, 0)  /* Color Frame Buffer Line Number */
 
+#define CLUT_SIZE      256
+
 #define CONSTA_MAX     0xFF            /* CONSTant Alpha MAX= 1.0 */
 #define BF1_PAXCA      0x600           /* Pixel Alpha x Constant Alpha */
 #define BF1_CA         0x400           /* Constant Alpha */
@@ -362,6 +364,28 @@ static irqreturn_t ltdc_irq(int irq, void *arg)
  * DRM_CRTC
  */
 
+static void ltdc_crtc_update_clut(struct drm_crtc *crtc)
+{
+       struct ltdc_device *ldev = crtc_to_ltdc(crtc);
+       struct drm_color_lut *lut;
+       u32 val;
+       int i;
+
+       if (!crtc || !crtc->state)
+               return;
+
+       if (!crtc->state->color_mgmt_changed || !crtc->state->gamma_lut)
+               return;
+
+       lut = (struct drm_color_lut *)crtc->state->gamma_lut->data;
+
+       for (i = 0; i < CLUT_SIZE; i++, lut++) {
+               val = ((lut->red << 8) & 0xff0000) | (lut->green & 0xff00) |
+                       (lut->blue >> 8) | (i << 24);
+               reg_write(ldev->regs, LTDC_L1CLUTWR, val);
+       }
+}
+
 static void ltdc_crtc_atomic_enable(struct drm_crtc *crtc,
                                    struct drm_crtc_state *old_state)
 {
@@ -485,6 +509,8 @@ static void ltdc_crtc_atomic_flush(struct drm_crtc *crtc,
 
        DRM_DEBUG_ATOMIC("\n");
 
+       ltdc_crtc_update_clut(crtc);
+
        /* Commit shadow registers = update planes at next vblank */
        reg_set(ldev->regs, LTDC_SRCR, SRCR_VBR);
 
@@ -532,6 +558,7 @@ void ltdc_crtc_disable_vblank(struct drm_device *ddev, 
unsigned int pipe)
        .reset = drm_atomic_helper_crtc_reset,
        .atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
        .atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
+       .gamma_set = drm_atomic_helper_legacy_gamma_set,
 };
 
 /*
@@ -764,6 +791,9 @@ static int ltdc_crtc_init(struct drm_device *ddev, struct 
drm_crtc *crtc)
 
        drm_crtc_helper_add(crtc, &ltdc_crtc_helper_funcs);
 
+       drm_mode_crtc_set_gamma_size(crtc, CLUT_SIZE);
+       drm_crtc_enable_color_mgmt(crtc, 0, false, CLUT_SIZE);
+
        DRM_DEBUG_DRIVER("CRTC:%d created\n", crtc->base.id);
 
        /* Add planes. Note : the first layer is used by primary plane */
-- 
1.9.1