The atomic_get_output_bus_fmts callback is used by the DRM bridge layer
to recursively select a suitable output format in a bridge chain.

As a bridge that outputs to HDMI, dw-hdmi-qp will have its output
formats determined by which formats the platform-specific integration of
the hardware supports, and the chosen HDMI output bit depth.

Implement this callback. The returned u32* buffer is supposed to be
freed by the caller of this callback, as specified by the callback's
documentation.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c | 64 ++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
index ab7fed6214e0..82a63964f7f7 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
@@ -11,6 +11,7 @@
 #include <linux/export.h>
 #include <linux/i2c.h>
 #include <linux/irq.h>
+#include <linux/media-bus-format.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/of.h>
@@ -862,6 +863,68 @@ static int dw_hdmi_qp_config_audio_infoframe(struct dw_hdmi_qp *hdmi,
 	return 0;
 }
 
+static u32*
+dw_hdmi_qp_bridge_get_output_bus_fmts(struct drm_bridge *bridge,
+				      struct drm_bridge_state *bridge_state,
+				      struct drm_crtc_state *crtc_state,
+				      struct drm_connector_state *conn_state,
+				      unsigned int *num_output_fmts)
+{
+	unsigned int num_fmts = 0;
+	u32 *out_fmts;
+
+	/*
+	 * bridge->supported_formats is a bit field of the HDMI_COLORSPACE_* enums.
+	 * These enums are defined by the HDMI standard, and currently top out at
+	 * 7. Consequently, BIT(7) is the highest bit that will be set here, unless
+	 * the standard runs out of reserved pixel formats. Therefore, hweight8()
+	 * will give an accurate count of how many bus formats we'll output.
+	 */
+	out_fmts = kmalloc_array(hweight8(bridge->supported_formats), sizeof(u32),
+				 GFP_KERNEL);
+	if (!out_fmts) {
+		*num_output_fmts = 0;
+		return NULL;
+	}
+
+	switch (conn_state->hdmi.output_bpc) {
+	case 12:
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_RGB))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_RGB121212_1X36;
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_YUV444))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_YUV12_1X36;
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_YUV422))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_UYVY12_1X24;
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_YUV420))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_UYYVYY12_0_5X36;
+		break;
+	case 10:
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_RGB))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_RGB101010_1X30;
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_YUV444))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_YUV10_1X30;
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_YUV422))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_UYVY10_1X20;
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_YUV420))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_UYYVYY10_0_5X30;
+		break;
+	default:
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_RGB))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_RGB888_1X24;
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_YUV444))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_YUV8_1X24;
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_YUV422))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_UYVY8_1X16;
+		if (bridge->supported_formats & BIT(HDMI_COLORSPACE_YUV420))
+			out_fmts[num_fmts++] = MEDIA_BUS_FMT_UYYVYY8_0_5X24;
+		break;
+	}
+
+	*num_output_fmts = num_fmts;
+
+	return out_fmts;
+}
+
 static void dw_hdmi_qp_bridge_atomic_enable(struct drm_bridge *bridge,
 					    struct drm_atomic_state *state)
 {
@@ -1213,6 +1276,7 @@ static int dw_hdmi_qp_cec_transmit(struct drm_bridge *bridge, u8 attempts,
 #endif /* CONFIG_DRM_DW_HDMI_QP_CEC */
 
 static const struct drm_bridge_funcs dw_hdmi_qp_bridge_funcs = {
+	.atomic_get_output_bus_fmts = dw_hdmi_qp_bridge_get_output_bus_fmts,
 	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
 	.atomic_reset = drm_atomic_helper_bridge_reset,

-- 
2.52.0