media: rockchip: rga: Only set output CSC mode for RGB input

Setting the output CSC mode is required for a YUV output, but must not
be set when the input is also YUV. Doing this (as tested with a YUV420P
to YUV420P conversion) results in wrong colors.

Adapt the logic to only set the output CSC mode when the output is YUV and
the input is RGB. Also add a comment to clarify the rationale.

Fixes: f7e7b48e ("[media] rockchip/rga: v4l2 m2m support")
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/platform/rockchip/rga/rga-hw.c

@@ -200,6 +200,11 @@ static void rga_cmd_set_trans_info(struct rga_ctx *ctx)
 	dst_info.data.format = ctx->out.fmt->hw_format;
 	dst_info.data.swap = ctx->out.fmt->color_swap;
 
+	/*
+	 * CSC mode must only be set when the colorspace families differ between
+	 * input and output. It must remain unset (zeroed) if both are the same.
+	 */
+
 	if (RGA_COLOR_FMT_IS_YUV(ctx->in.fmt->hw_format) &&
 	    RGA_COLOR_FMT_IS_RGB(ctx->out.fmt->hw_format)) {
 		switch (ctx->in.colorspace) {
@@ -212,7 +217,8 @@ static void rga_cmd_set_trans_info(struct rga_ctx *ctx)
 		}
 	}
 
-	if (RGA_COLOR_FMT_IS_YUV(ctx->out.fmt->hw_format)) {
+	if (RGA_COLOR_FMT_IS_RGB(ctx->in.fmt->hw_format) &&
+	    RGA_COLOR_FMT_IS_YUV(ctx->out.fmt->hw_format)) {
 		switch (ctx->out.colorspace) {
 		case V4L2_COLORSPACE_REC709:
 			dst_info.data.csc_mode = RGA_SRC_CSC_MODE_BT709_R0;