drm: atmel-hlcdc: Support inverting the pixel clock polarity

On the SoC host controller, the pixel clock can be:
* standard: data is launched on the rising edge
* inverted: data is launched on the falling edge

Some panels may need the inverted option to be used so let's support
this DRM flag.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230609144843.851327-1-miquel.raynal@bootlin.com

Author: miquelraynal

drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c

@@ -68,14 +68,35 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc *c)
 	struct atmel_hlcdc_crtc *crtc = drm_crtc_to_atmel_hlcdc_crtc(c);
 	struct regmap *regmap = crtc->dc->hlcdc->regmap;
 	struct drm_display_mode *adj = &c->state->adjusted_mode;
+	struct drm_encoder *encoder = NULL, *en_iter;
+	struct drm_connector *connector = NULL;
 	struct atmel_hlcdc_crtc_state *state;
+	struct drm_device *ddev = c->dev;
+	struct drm_connector_list_iter iter;
 	unsigned long mode_rate;
 	struct videomode vm;
 	unsigned long prate;
 	unsigned int mask = ATMEL_HLCDC_CLKDIV_MASK | ATMEL_HLCDC_CLKPOL;
 	unsigned int cfg = 0;
 	int div, ret;
 
+	/* get encoder from crtc */
+	drm_for_each_encoder(en_iter, ddev) {
+		if (en_iter->crtc == c) {
+			encoder = en_iter;
+			break;
+		}
+	}
+
+	if (encoder) {
+		/* Get the connector from encoder */
+		drm_connector_list_iter_begin(ddev, &iter);
+		drm_for_each_connector_iter(connector, &iter)
+			if (connector->encoder == encoder)
+				break;
+		drm_connector_list_iter_end(&iter);
+	}
+
 	ret = clk_prepare_enable(crtc->dc->hlcdc->sys_clk);
 	if (ret)
 		return;
@@ -134,6 +155,10 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc *c)
 
 	cfg |= ATMEL_HLCDC_CLKDIV(div);
 
+	if (connector &&
+	    connector->display_info.bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
+		cfg |= ATMEL_HLCDC_CLKPOL;
+
 	regmap_update_bits(regmap, ATMEL_HLCDC_CFG(0), mask, cfg);
 
 	state = drm_crtc_state_to_atmel_hlcdc_crtc_state(c->state);