drm/msm/mdp4: add lcdc-align-lsb flag to control lane alignment

This allows controlling which of the 8 lanes are used for 6 bit color.
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>

Documentation/devicetree/bindings/display/msm/mdp4.txt

@@ -38,6 +38,8 @@ Required properties:
 Optional properties:
 - clock-names: the following clocks are optional:
   * "lut_clk"
+- qcom,lcdc-align-lsb: Boolean value indicating that LSB alignment should be
+  used for LCDC. This is only valid for 18bpp panels.
 
 Example:
 

drivers/gpu/drm/msm/disp/mdp4/mdp4_lcdc_encoder.c

@@ -377,20 +377,25 @@ static void mdp4_lcdc_encoder_enable(struct drm_encoder *encoder)
 	unsigned long pc = mdp4_lcdc_encoder->pixclock;
 	struct mdp4_kms *mdp4_kms = get_kms(encoder);
 	struct drm_panel *panel;
+	uint32_t config;
 	int i, ret;
 
 	if (WARN_ON(mdp4_lcdc_encoder->enabled))
 		return;
 
 	/* TODO: hard-coded for 18bpp: */
-	mdp4_crtc_set_config(encoder->crtc,
-			MDP4_DMA_CONFIG_R_BPC(BPC6) |
-			MDP4_DMA_CONFIG_G_BPC(BPC6) |
-			MDP4_DMA_CONFIG_B_BPC(BPC6) |
-			MDP4_DMA_CONFIG_PACK_ALIGN_MSB |
-			MDP4_DMA_CONFIG_PACK(0x21) |
-			MDP4_DMA_CONFIG_DEFLKR_EN |
-			MDP4_DMA_CONFIG_DITHER_EN);
+	config =
+		MDP4_DMA_CONFIG_R_BPC(BPC6) |
+		MDP4_DMA_CONFIG_G_BPC(BPC6) |
+		MDP4_DMA_CONFIG_B_BPC(BPC6) |
+		MDP4_DMA_CONFIG_PACK(0x21) |
+		MDP4_DMA_CONFIG_DEFLKR_EN |
+		MDP4_DMA_CONFIG_DITHER_EN;
+
+	if (!of_property_read_bool(dev->dev->of_node, "qcom,lcdc-align-lsb"))
+		config |= MDP4_DMA_CONFIG_PACK_ALIGN_MSB;
+
+	mdp4_crtc_set_config(encoder->crtc, config);
 	mdp4_crtc_set_intf(encoder->crtc, INTF_LCDC_DTV, 0);
 
 	bs_set(mdp4_lcdc_encoder, 1);