drm/vkms: Add support for writeback

This patch implements the necessary functions to add writeback support
for vkms. This feature is useful for testing compositors if you don't
have hardware with writeback support.

Change in V4 (Emil and Melissa):
- Move signal completion above drm_crtc_add_crc_entry()
- Make writeback always available
- Use appropriate namespace
- Drop fb check in vkms_wb_atomic_commit
- Make vkms_set_composer visible for writeback code
- Enable composer operation on prepare_job and disable it on cleanup_job
- Drop extra space at the end of the file
- Rebase

Change in V3 (Daniel):
- If writeback is enabled, compose everything into the writeback buffer
instead of CRC private buffer
- Guarantees that the CRC will match exactly what we have in the
writeback buffer.

Change in V2:
- Rework signal completion (Brian)
- Integrates writeback with active_planes (Daniel)
- Compose cursor (Daniel)

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200830142000.146706-4-rodrigosiqueiramelo@gmail.com

drivers/gpu/drm/vkms/Makefile

@@ -1,4 +1,11 @@
 # SPDX-License-Identifier: GPL-2.0-only
-vkms-y := vkms_drv.o vkms_plane.o vkms_output.o vkms_crtc.o vkms_gem.o vkms_composer.o
+vkms-y := \
+	vkms_drv.o \
+	vkms_plane.o \
+	vkms_output.o \
+	vkms_crtc.o \
+	vkms_gem.o \
+	vkms_composer.o \
+	vkms_writeback.o
 
 obj-$(CONFIG_DRM_VKMS) += vkms.o

drivers/gpu/drm/vkms/vkms_composer.c

@@ -186,16 +186,17 @@ void vkms_composer_worker(struct work_struct *work)
 	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
 	struct vkms_composer *primary_composer = NULL;
 	struct vkms_composer *cursor_composer = NULL;
+	bool crc_pending, wb_pending;
 	void *vaddr_out = NULL;
 	u32 crc32 = 0;
 	u64 frame_start, frame_end;
-	bool crc_pending;
 	int ret;
 
 	spin_lock_irq(&out->composer_lock);
 	frame_start = crtc_state->frame_start;
 	frame_end = crtc_state->frame_end;
 	crc_pending = crtc_state->crc_pending;
+	wb_pending = crtc_state->wb_pending;
 	crtc_state->frame_start = 0;
 	crtc_state->frame_end = 0;
 	crtc_state->crc_pending = false;
@@ -217,22 +218,32 @@ void vkms_composer_worker(struct work_struct *work)
 	if (!primary_composer)
 		return;
 
+	if (wb_pending)
+		vaddr_out = crtc_state->active_writeback;
+
 	ret = compose_planes(&vaddr_out, primary_composer, cursor_composer);
 	if (ret) {
-		if (ret == -EINVAL)
+		if (ret == -EINVAL && !wb_pending)
 			kfree(vaddr_out);
 		return;
 	}
 
 	crc32 = compute_crc(vaddr_out, primary_composer);
 
+	if (wb_pending) {
+		drm_writeback_signal_completion(&out->wb_connector, 0);
+		spin_lock_irq(&out->composer_lock);
+		crtc_state->wb_pending = false;
+		spin_unlock_irq(&out->composer_lock);
+	} else {
+		kfree(vaddr_out);
+	}
+
 	/*
 	 * The worker can fall behind the vblank hrtimer, make sure we catch up.
 	 */
 	while (frame_start <= frame_end)
 		drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32);
-
-	kfree(vaddr_out);
 }
 
 static const char * const pipe_crc_sources[] = {"auto"};
@@ -275,7 +286,7 @@ int vkms_verify_crc_source(struct drm_crtc *crtc, const char *src_name,
 	return 0;
 }
 
-static void vkms_set_composer(struct vkms_output *out, bool enabled)
+void vkms_set_composer(struct vkms_output *out, bool enabled)
 {
 	bool old_enabled;
 

drivers/gpu/drm/vkms/vkms_drv.h

@@ -8,6 +8,7 @@
 #include <drm/drm.h>
 #include <drm/drm_gem.h>
 #include <drm/drm_encoder.h>
+#include <drm/drm_writeback.h>
 
 #define XRES_MIN    20
 #define YRES_MIN    20
@@ -52,9 +53,11 @@ struct vkms_crtc_state {
 	int num_active_planes;
 	/* stack of active planes for crc computation, should be in z order */
 	struct vkms_plane_state **active_planes;
+	void *active_writeback;
 
-	/* below three are protected by vkms_output.composer_lock */
+	/* below four are protected by vkms_output.composer_lock */
 	bool crc_pending;
+	bool wb_pending;
 	u64 frame_start;
 	u64 frame_end;
 };
@@ -63,6 +66,7 @@ struct vkms_output {
 	struct drm_crtc crtc;
 	struct drm_encoder encoder;
 	struct drm_connector connector;
+	struct drm_writeback_connector wb_connector;
 	struct hrtimer vblank_hrtimer;
 	ktime_t period_ns;
 	struct drm_pending_vblank_event *event;
@@ -143,5 +147,9 @@ int vkms_verify_crc_source(struct drm_crtc *crtc, const char *source_name,
 
 /* Composer Support */
 void vkms_composer_worker(struct work_struct *work);
+void vkms_set_composer(struct vkms_output *out, bool enabled);
+
+/* Writeback */
+int vkms_enable_writeback_connector(struct vkms_device *vkmsdev);
 
 #endif /* _VKMS_DRV_H_ */

drivers/gpu/drm/vkms/vkms_output.c

@@ -80,6 +80,10 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
 		goto err_attach;
 	}
 
+	ret = vkms_enable_writeback_connector(vkmsdev);
+	if (ret)
+		DRM_ERROR("Failed to init writeback connector\n");
+
 	drm_mode_config_reset(dev);
 
 	return 0;

drivers/gpu/drm/vkms/vkms_writeback.c

@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include "vkms_drv.h"
+#include <drm/drm_fourcc.h>
+#include <drm/drm_writeback.h>
+#include <drm/drm_probe_helper.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_gem_framebuffer_helper.h>
+
+static const u32 vkms_wb_formats[] = {
+	DRM_FORMAT_XRGB8888,
+};
+
+static const struct drm_connector_funcs vkms_wb_connector_funcs = {
+	.fill_modes = drm_helper_probe_single_connector_modes,
+	.destroy = drm_connector_cleanup,
+	.reset = drm_atomic_helper_connector_reset,
+	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
+};
+
+static int vkms_wb_encoder_atomic_check(struct drm_encoder *encoder,
+					struct drm_crtc_state *crtc_state,
+					struct drm_connector_state *conn_state)
+{
+	struct drm_framebuffer *fb;
+	const struct drm_display_mode *mode = &crtc_state->mode;
+
+	if (!conn_state->writeback_job || !conn_state->writeback_job->fb)
+		return 0;
+
+	fb = conn_state->writeback_job->fb;
+	if (fb->width != mode->hdisplay || fb->height != mode->vdisplay) {
+		DRM_DEBUG_KMS("Invalid framebuffer size %ux%u\n",
+			      fb->width, fb->height);
+		return -EINVAL;
+	}
+
+	if (fb->format->format != vkms_wb_formats[0]) {
+		struct drm_format_name_buf format_name;
+
+		DRM_DEBUG_KMS("Invalid pixel format %s\n",
+			      drm_get_format_name(fb->format->format,
+						  &format_name));
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static const struct drm_encoder_helper_funcs vkms_wb_encoder_helper_funcs = {
+	.atomic_check = vkms_wb_encoder_atomic_check,
+};
+
+static int vkms_wb_connector_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 vkms_wb_prepare_job(struct drm_writeback_connector *wb_connector,
+			       struct drm_writeback_job *job)
+{
+	struct vkms_gem_object *vkms_obj;
+	struct drm_gem_object *gem_obj;
+	int ret;
+
+	if (!job->fb)
+		return 0;
+
+	gem_obj = drm_gem_fb_get_obj(job->fb, 0);
+	ret = vkms_gem_vmap(gem_obj);
+	if (ret) {
+		DRM_ERROR("vmap failed: %d\n", ret);
+		return ret;
+	}
+
+	vkms_obj = drm_gem_to_vkms_gem(gem_obj);
+	job->priv = vkms_obj->vaddr;
+
+	return 0;
+}
+
+static void vkms_wb_cleanup_job(struct drm_writeback_connector *connector,
+				struct drm_writeback_job *job)
+{
+	struct drm_gem_object *gem_obj;
+	struct vkms_device *vkmsdev;
+
+	if (!job->fb)
+		return;
+
+	gem_obj = drm_gem_fb_get_obj(job->fb, 0);
+	vkms_gem_vunmap(gem_obj);
+
+	vkmsdev = drm_device_to_vkms_device(gem_obj->dev);
+	vkms_set_composer(&vkmsdev->output, false);
+}
+
+static void vkms_wb_atomic_commit(struct drm_connector *conn,
+				  struct drm_connector_state *state)
+{
+	struct vkms_device *vkmsdev = drm_device_to_vkms_device(conn->dev);
+	struct vkms_output *output = &vkmsdev->output;
+	struct drm_writeback_connector *wb_conn = &output->wb_connector;
+	struct drm_connector_state *conn_state = wb_conn->base.state;
+	struct vkms_crtc_state *crtc_state = output->composer_state;
+
+	if (!conn_state)
+		return;
+
+	vkms_set_composer(&vkmsdev->output, true);
+
+	spin_lock_irq(&output->composer_lock);
+	crtc_state->active_writeback = conn_state->writeback_job->priv;
+	crtc_state->wb_pending = true;
+	spin_unlock_irq(&output->composer_lock);
+	drm_writeback_queue_job(wb_conn, state);
+}
+
+static const struct drm_connector_helper_funcs vkms_wb_conn_helper_funcs = {
+	.get_modes = vkms_wb_connector_get_modes,
+	.prepare_writeback_job = vkms_wb_prepare_job,
+	.cleanup_writeback_job = vkms_wb_cleanup_job,
+	.atomic_commit = vkms_wb_atomic_commit,
+};
+
+int vkms_enable_writeback_connector(struct vkms_device *vkmsdev)
+{
+	struct drm_writeback_connector *wb = &vkmsdev->output.wb_connector;
+
+	vkmsdev->output.wb_connector.encoder.possible_crtcs = 1;
+	drm_connector_helper_add(&wb->base, &vkms_wb_conn_helper_funcs);
+
+	return drm_writeback_connector_init(&vkmsdev->drm, wb,
+					    &vkms_wb_connector_funcs,
+					    &vkms_wb_encoder_helper_funcs,
+					    vkms_wb_formats,
+					    ARRAY_SIZE(vkms_wb_formats));
+}