drm/meson: venc: add support for YUV420 setup

This patch adds encoding support for the YUV420 output from the
Amlogic Meson SoCs Video Processing Unit to the HDMI Controller.

The YUV420 is obtained by generating a YUV444 pixel stream like
the classic HDMI display modes, but then the Video Encoder output
can be configured to down-sample the YUV444 pixel stream to a YUV420
stream.

In addition if pixel stream down-sampling, the Y Cb Cr components must
also be mapped differently to align with the HDMI2.0 specifications.

Signed-off-by: Neil Armstrong <[e-mail]>
Reviewed-by: Jernej Škrabec <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/meson/meson_dw_hdmi.c

···
 	DRM_DEBUG_DRIVER("\"%s\" vic %d\n", mode->name, vic);
 
 	/* VENC + VENC-DVI Mode setup */
-	meson_venc_hdmi_mode_set(priv, vic, mode);
+	meson_venc_hdmi_mode_set(priv, vic, ycrcb_map, false,
+				 VPU_HDMI_OUTPUT_CBYCR);
 
 	/* VCLK Set clock */
 	dw_hdmi_set_vclk(dw_hdmi, mode);

drivers/gpu/drm/meson/meson_venc.c

···
 EXPORT_SYMBOL_GPL(meson_venc_hdmi_venc_repeat);
 
 void meson_venc_hdmi_mode_set(struct meson_drm *priv, int vic,
+			      unsigned int ycrcb_map,
+			      bool yuv420_mode,
 			      const struct drm_display_mode *mode)
 {
 	union meson_hdmi_venc_mode *vmode = NULL;
···
 	if (mode->flags & DRM_MODE_FLAG_PVSYNC)
 		reg |= VPU_HDMI_INV_VSYNC;
 
-	/* Output data format: CbYCr */
-	reg |= VPU_HDMI_OUTPUT_CBYCR;
+	/* Output data format */
+	reg |= ycrcb_map;
 
 	/*
 	 * Write rate to the async FIFO between VENC and HDMI.
 	 * One write every 2 wr_clk.
 	 */
-	if (venc_repeat)
+	if (venc_repeat || yuv420_mode)
 		reg |= VPU_HDMI_WR_RATE(2);
 
 	/*

drivers/gpu/drm/meson/meson_venc.h

···
 void meson_venci_cvbs_mode_set(struct meson_drm *priv,
 			       struct meson_cvbs_enci_mode *mode);
 void meson_venc_hdmi_mode_set(struct meson_drm *priv, int vic,
+			      unsigned int ycrcb_map,
+			      bool yuv420_mode,
 			      const struct drm_display_mode *mode);
 unsigned int meson_venci_get_field(struct meson_drm *priv);