--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * rcar_du_writeback.c  --  R-Car Display Unit Writeback Support
+ *
+ * Copyright (C) 2019 Laurent Pinchart <laurent.pinchart@ideasonboard.com>
+ */
+
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_device.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_probe_helper.h>
+#include <drm/drm_writeback.h>
+
+#include "rcar_du_crtc.h"
+#include "rcar_du_drv.h"
+#include "rcar_du_kms.h"
+
+/**
+ * struct rcar_du_wb_conn_state - Driver-specific writeback connector state
+ * @state: base DRM connector state
+ * @format: format of the writeback framebuffer
+ */
+struct rcar_du_wb_conn_state {
+       struct drm_connector_state state;
+       const struct rcar_du_format_info *format;
+};
+
+#define to_rcar_wb_conn_state(s) \
+       container_of(s, struct rcar_du_wb_conn_state, state)
+
+/**
+ * struct rcar_du_wb_job - Driver-private data for writeback jobs
+ * @sg_tables: scatter-gather tables for the framebuffer memory
+ */
+struct rcar_du_wb_job {
+       struct sg_table sg_tables[3];
+};
+
+static int rcar_du_wb_conn_get_modes(struct drm_connector *connector)
+{
+       struct drm_device *dev = connector->dev;
+
+       return drm_add_modes_noedid(connector, dev->mode_config.max_width,
+                                   dev->mode_config.max_height);
+}
+
+static int rcar_du_wb_prepare_job(struct drm_writeback_connector *connector,
+                                 struct drm_writeback_job *job)
+{
+       struct rcar_du_crtc *rcrtc = wb_to_rcar_crtc(connector);
+       struct rcar_du_wb_job *rjob;
+       int ret;
+
+       if (!job->fb)
+               return 0;
+
+       rjob = kzalloc(sizeof(*rjob), GFP_KERNEL);
+       if (!rjob)
+               return -ENOMEM;
+
+       /* Map the framebuffer to the VSP. */
+       ret = rcar_du_vsp_map_fb(rcrtc->vsp, job->fb, rjob->sg_tables);
+       if (ret < 0) {
+               kfree(rjob);
+               return ret;
+       }
+
+       job->priv = rjob;
+       return 0;
+}
+
+static void rcar_du_wb_cleanup_job(struct drm_writeback_connector *connector,
+                                  struct drm_writeback_job *job)
+{
+       struct rcar_du_crtc *rcrtc = wb_to_rcar_crtc(connector);
+       struct rcar_du_wb_job *rjob = job->priv;
+
+       if (!job->fb)
+               return;
+
+       rcar_du_vsp_unmap_fb(rcrtc->vsp, job->fb, rjob->sg_tables);
+       kfree(rjob);
+}
+
+static const struct drm_connector_helper_funcs rcar_du_wb_conn_helper_funcs = {
+       .get_modes = rcar_du_wb_conn_get_modes,
+       .prepare_writeback_job = rcar_du_wb_prepare_job,
+       .cleanup_writeback_job = rcar_du_wb_cleanup_job,
+};
+
+static struct drm_connector_state *
+rcar_du_wb_conn_duplicate_state(struct drm_connector *connector)
+{
+       struct rcar_du_wb_conn_state *copy;
+
+       if (WARN_ON(!connector->state))
+               return NULL;
+
+       copy = kzalloc(sizeof(*copy), GFP_KERNEL);
+       if (!copy)
+               return NULL;
+
+       __drm_atomic_helper_connector_duplicate_state(connector, ©->state);
+
+       return ©->state;
+}
+
+static void rcar_du_wb_conn_destroy_state(struct drm_connector *connector,
+                                         struct drm_connector_state *state)
+{
+       __drm_atomic_helper_connector_destroy_state(state);
+       kfree(to_rcar_wb_conn_state(state));
+}
+
+static void rcar_du_wb_conn_reset(struct drm_connector *connector)
+{
+       struct rcar_du_wb_conn_state *state;
+
+       if (connector->state) {
+               rcar_du_wb_conn_destroy_state(connector, connector->state);
+               connector->state = NULL;
+       }
+
+       state = kzalloc(sizeof(*state), GFP_KERNEL);
+       if (state == NULL)
+               return;
+
+       __drm_atomic_helper_connector_reset(connector, &state->state);
+}
+
+static const struct drm_connector_funcs rcar_du_wb_conn_funcs = {
+       .reset = rcar_du_wb_conn_reset,
+       .fill_modes = drm_helper_probe_single_connector_modes,
+       .destroy = drm_connector_cleanup,
+       .atomic_duplicate_state = rcar_du_wb_conn_duplicate_state,
+       .atomic_destroy_state = rcar_du_wb_conn_destroy_state,
+};
+
+static int rcar_du_wb_enc_atomic_check(struct drm_encoder *encoder,
+                                      struct drm_crtc_state *crtc_state,
+                                      struct drm_connector_state *conn_state)
+{
+       struct rcar_du_wb_conn_state *wb_state =
+               to_rcar_wb_conn_state(conn_state);
+       const struct drm_display_mode *mode = &crtc_state->mode;
+       struct drm_device *dev = encoder->dev;
+       struct drm_framebuffer *fb;
+
+       if (!conn_state->writeback_job || !conn_state->writeback_job->fb)
+               return 0;
+
+       fb = conn_state->writeback_job->fb;
+
+       /*
+        * Verify that the framebuffer format is supported and that its size
+        * matches the current mode.
+        */
+       if (fb->width != mode->hdisplay || fb->height != mode->vdisplay) {
+               dev_dbg(dev->dev, "%s: invalid framebuffer size %ux%u\n",
+                       __func__, fb->width, fb->height);
+               return -EINVAL;
+       }
+
+       wb_state->format = rcar_du_format_info(fb->format->format);
+       if (wb_state->format == NULL) {
+               dev_dbg(dev->dev, "%s: unsupported format %08x\n", __func__,
+                       fb->format->format);
+               return -EINVAL;
+       }
+
+       return 0;
+}
+
+static const struct drm_encoder_helper_funcs rcar_du_wb_enc_helper_funcs = {
+       .atomic_check = rcar_du_wb_enc_atomic_check,
+};
+
+/*
+ * Only RGB formats are currently supported as the VSP outputs RGB to the DU
+ * and can't convert to YUV separately for writeback.
+ */
+static const u32 writeback_formats[] = {
+       DRM_FORMAT_RGB332,
+       DRM_FORMAT_ARGB4444,
+       DRM_FORMAT_XRGB4444,
+       DRM_FORMAT_ARGB1555,
+       DRM_FORMAT_XRGB1555,
+       DRM_FORMAT_RGB565,
+       DRM_FORMAT_BGR888,
+       DRM_FORMAT_RGB888,
+       DRM_FORMAT_BGRA8888,
+       DRM_FORMAT_BGRX8888,
+       DRM_FORMAT_ARGB8888,
+       DRM_FORMAT_XRGB8888,
+};
+
+int rcar_du_writeback_init(struct rcar_du_device *rcdu,
+                          struct rcar_du_crtc *rcrtc)
+{
+       struct drm_writeback_connector *wb_conn = &rcrtc->writeback;
+
+       wb_conn->encoder.possible_crtcs = 1 << drm_crtc_index(&rcrtc->crtc);
+       drm_connector_helper_add(&wb_conn->base,
+                                &rcar_du_wb_conn_helper_funcs);
+
+       return drm_writeback_connector_init(rcdu->ddev, wb_conn,
+                                           &rcar_du_wb_conn_funcs,
+                                           &rcar_du_wb_enc_helper_funcs,
+                                           writeback_formats,
+                                           ARRAY_SIZE(writeback_formats));
+}
+
+void rcar_du_writeback_setup(struct rcar_du_crtc *rcrtc,
+                            struct vsp1_du_writeback_config *cfg)
+{
+       struct rcar_du_wb_conn_state *wb_state;
+       struct drm_connector_state *state;
+       struct rcar_du_wb_job *rjob;
+       struct drm_framebuffer *fb;
+       unsigned int i;
+
+       state = rcrtc->writeback.base.state;
+       if (!state || !state->writeback_job || !state->writeback_job->fb)
+               return;
+
+       fb = state->writeback_job->fb;
+       rjob = state->writeback_job->priv;
+       wb_state = to_rcar_wb_conn_state(state);
+
+       cfg->pixelformat = wb_state->format->v4l2;
+       cfg->pitch = fb->pitches[0];
+
+       for (i = 0; i < wb_state->format->planes; ++i)
+               cfg->mem[i] = sg_dma_address(rjob->sg_tables[i].sgl)
+                           + fb->offsets[i];
+
+       drm_writeback_queue_job(&rcrtc->writeback, state);
+}
+
+void rcar_du_writeback_complete(struct rcar_du_crtc *rcrtc)
+{
+       drm_writeback_signal_completion(&rcrtc->writeback, 0);
+}