[PATCH v3] drm/mxsfb: use bus_format to determine LCD bus width

[Stefan Agner]

The LCD bus width does not need to align with the pixel format. The
LCDIF controller automatically converts between pixel formats and
bus width by padding or dropping LSBs.

The DRM subsystem has the notion of bus_format which allows to
determine what bus_formats are supported by the display. Choose the
first available or fallback to 24 bit if none are available.

Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
---
Changes in v3:
- Use read-modify-write to update the LCDC_CTRL field
Changes in v2:
- Use seperate function mxsfb_set_bus_fmt

 drivers/gpu/drm/mxsfb/mxsfb_crtc.c | 34 ++++++++++++++++++++++++++++++++--
 drivers/gpu/drm/mxsfb/mxsfb_regs.h |  1 +
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
index 7f21eb3..22512f3 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
@@ -65,13 +65,11 @@ static int mxsfb_set_pixel_fmt(struct mxsfb_drm_private *mxsfb)
 	switch (format) {
 	case DRM_FORMAT_RGB565:
 		dev_dbg(drm->dev, "Setting up RGB565 mode\n");
-		ctrl |= CTRL_SET_BUS_WIDTH(STMLCDIF_16BIT);
 		ctrl |= CTRL_SET_WORD_LENGTH(0);
 		ctrl1 |= CTRL1_SET_BYTE_PACKAGING(0xf);
 		break;
 	case DRM_FORMAT_XRGB8888:
 		dev_dbg(drm->dev, "Setting up XRGB8888 mode\n");
-		ctrl |= CTRL_SET_BUS_WIDTH(STMLCDIF_24BIT);
 		ctrl |= CTRL_SET_WORD_LENGTH(3);
 		/* Do not use packed pixels = one pixel per word instead. */
 		ctrl1 |= CTRL1_SET_BYTE_PACKAGING(0x7);
@@ -87,6 +85,36 @@ static int mxsfb_set_pixel_fmt(struct mxsfb_drm_private *mxsfb)
 	return 0;
 }
 
+static void mxsfb_set_bus_fmt(struct mxsfb_drm_private *mxsfb)
+{
+	struct drm_crtc *crtc = &mxsfb->pipe.crtc;
+	struct drm_device *drm = crtc->dev;
+	u32 bus_format = MEDIA_BUS_FMT_RGB888_1X24;
+	u32 reg;
+
+	reg = readl(mxsfb->base + LCDC_CTRL);
+
+	if (mxsfb->connector.display_info.num_bus_formats)
+		bus_format = mxsfb->connector.display_info.bus_formats[0];
+
+	reg &= ~CTRL_BUS_WIDTH_MASK;
+	switch (bus_format) {
+	case MEDIA_BUS_FMT_RGB565_1X16:
+		reg |= CTRL_SET_BUS_WIDTH(STMLCDIF_16BIT);
+		break;
+	case MEDIA_BUS_FMT_RGB666_1X18:
+		reg |= CTRL_SET_BUS_WIDTH(STMLCDIF_18BIT);
+		break;
+	case MEDIA_BUS_FMT_RGB888_1X24:
+		reg |= CTRL_SET_BUS_WIDTH(STMLCDIF_24BIT);
+		break;
+	default:
+		dev_err(drm->dev, "Unknown media bus format %d\n", bus_format);
+		break;
+	}
+	writel(reg, mxsfb->base + LCDC_CTRL);
+}
+
 static void mxsfb_enable_controller(struct mxsfb_drm_private *mxsfb)
 {
 	u32 reg;
@@ -182,6 +210,8 @@ static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
 
 	writel(vdctrl0, mxsfb->base + LCDC_VDCTRL0);
 
+	mxsfb_set_bus_fmt(mxsfb);
+
 	/* Frame length in lines. */
 	writel(m->crtc_vtotal, mxsfb->base + LCDC_VDCTRL1);
 
diff --git a/drivers/gpu/drm/mxsfb/mxsfb_regs.h b/drivers/gpu/drm/mxsfb/mxsfb_regs.h
index 31d62cd..66a6ba9 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_regs.h
+++ b/drivers/gpu/drm/mxsfb/mxsfb_regs.h
@@ -44,6 +44,7 @@
 #define CTRL_DATA_SELECT		(1 << 16)
 #define CTRL_SET_BUS_WIDTH(x)		(((x) & 0x3) << 10)
 #define CTRL_GET_BUS_WIDTH(x)		(((x) >> 10) & 0x3)
+#define CTRL_BUS_WIDTH_MASK		(0x3 << 10)
 #define CTRL_SET_WORD_LENGTH(x)		(((x) & 0x3) << 8)
 #define CTRL_GET_WORD_LENGTH(x)		(((x) >> 8) & 0x3)
 #define CTRL_MASTER			(1 << 5)
-- 
2.10.2