[RFC] drm/vkms: Add writeback support

[Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>]

Hi,

I started to work for add the writeback feature into the VKMS, and this
RFC represents my first draft. As a result, I have some questions which
I list below.

1. In this patch, I replaced the virtual connector by the writeback
connector. Is it a good idea? Or should I keep both connectors? If I
keep both connectors, should I add a module parameter to enable the
writeback?

2. When I added the writeback connector (in
drm_writeback_connector_init()), I noticed that I had to indicate the
struct drm_encoder_helper_funcs. However, I think that VKMS does not
need anything sophisticated related to encoders at the writeback
perspective. Am I right? Or did I missed something?

3. I just discovered that the writeback connectors are not exposed as a
connector for the userspace, as a result, IGT tests do not work and
Wayland is unable to run as well. Simon Ser and Daniel Stone, explained
to me that I have to update the compositor (in my case Weston) to set
DRM_CLIENT_CAP_WRITEBACK_CONNECTORS via drmSetClientCap(). Since I do
not have experience with userspace, anyone can point me out another
aspect that I have to take a look to make the writeback work in the user
space? Also, Is it possible to update the IGT test or do I need to
create a new set of tests?

Thanks!

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
---
 drivers/gpu/drm/vkms/vkms_crc.c    |   9 ++-
 drivers/gpu/drm/vkms/vkms_crtc.c   |   2 +
 drivers/gpu/drm/vkms/vkms_drv.h    |   3 +-
 drivers/gpu/drm/vkms/vkms_output.c | 107 +++++++++++++++++++++--------
 4 files changed, 89 insertions(+), 32 deletions(-)

diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c
index 9d9e8146db90..5d9ac45e00f2 100644
--- a/drivers/gpu/drm/vkms/vkms_crc.c
+++ b/drivers/gpu/drm/vkms/vkms_crc.c
@@ -109,7 +109,8 @@ static void compose_cursor(struct vkms_crc_data *cursor_crc,
 }
 
 static uint32_t _vkms_get_crc(struct vkms_crc_data *primary_crc,
-			      struct vkms_crc_data *cursor_crc)
+			      struct vkms_crc_data *cursor_crc,
+			      struct vkms_output *out)
 {
 	struct drm_framebuffer *fb = &primary_crc->fb;
 	struct drm_gem_object *gem_obj = drm_gem_fb_get_obj(fb, 0);
@@ -130,6 +131,10 @@ static uint32_t _vkms_get_crc(struct vkms_crc_data *primary_crc,
 	}
 
 	memcpy(vaddr_out, vkms_obj->vaddr, vkms_obj->gem.size);
+	// TODO: Remove this copy from crc, and make this sort of operation
+	// generic since we can use in different places
+	memcpy(out->connector.base.state->writeback_job->fb,
+	       vkms_obj->vaddr, vkms_obj->gem.size);
 	mutex_unlock(&vkms_obj->pages_lock);
 
 	if (cursor_crc)
@@ -193,7 +198,7 @@ void vkms_crc_work_handle(struct work_struct *work)
 	}
 
 	if (primary_crc)
-		crc32 = _vkms_get_crc(primary_crc, cursor_crc);
+		crc32 = _vkms_get_crc(primary_crc, cursor_crc, out);
 
 	frame_end = drm_crtc_accurate_vblank_count(crtc);
 
diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
index 177bbcb38306..d33ddcc40a29 100644
--- a/drivers/gpu/drm/vkms/vkms_crtc.c
+++ b/drivers/gpu/drm/vkms/vkms_crtc.c
@@ -48,6 +48,8 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
 
 	_vblank_handle(output);
 
+	drm_writeback_signal_completion(&output->connector, 0);
+
 	ret_overrun = hrtimer_forward_now(&output->vblank_hrtimer,
 					  output->period_ns);
 
diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
index 1c93990693e3..1e8184ad872f 100644
--- a/drivers/gpu/drm/vkms/vkms_drv.h
+++ b/drivers/gpu/drm/vkms/vkms_drv.h
@@ -5,6 +5,7 @@
 #include <drm/drm.h>
 #include <drm/drm_gem.h>
 #include <drm/drm_encoder.h>
+#include <drm/drm_writeback.h>
 #include <linux/hrtimer.h>
 
 #define XRES_MIN    20
@@ -61,7 +62,7 @@ struct vkms_crtc_state {
 struct vkms_output {
 	struct drm_crtc crtc;
 	struct drm_encoder encoder;
-	struct drm_connector connector;
+	struct drm_writeback_connector connector;
 	struct hrtimer vblank_hrtimer;
 	ktime_t period_ns;
 	struct drm_pending_vblank_event *event;
diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
index 271a0eb9042c..46622d012107 100644
--- a/drivers/gpu/drm/vkms/vkms_output.c
+++ b/drivers/gpu/drm/vkms/vkms_output.c
@@ -9,6 +9,13 @@
 #include "vkms_drv.h"
 #include <drm/drm_crtc_helper.h>
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_writeback.h>
+
+#define to_wb_state(_state) (struct vkms_writeback_connector_state *)(_state)
+
+struct vkms_writeback_connector_state {
+	struct drm_connector_state base;
+};
 
 static void vkms_connector_destroy(struct drm_connector *connector)
 {
@@ -16,11 +23,48 @@ static void vkms_connector_destroy(struct drm_connector *connector)
 	drm_connector_cleanup(connector);
 }
 
+static void vkms_connector_reset(struct drm_connector *connector)
+{
+	struct vkms_writeback_connector_state *wb_state =
+		kzalloc(sizeof(*wb_state), GFP_KERNEL);
+
+	if (connector->state)
+		__drm_atomic_helper_connector_destroy_state(connector->state);
+
+	kfree(connector->state);
+	__drm_atomic_helper_connector_reset(connector, &wb_state->base);
+}
+
+static struct drm_connector_state *
+vkms_connector_duplicate_state(struct drm_connector *connector)
+{
+	struct vkms_writeback_connector_state *wb_state;
+
+	if (WARN_ON(!connector->state))
+		return NULL;
+
+	wb_state = kzalloc(sizeof(*wb_state), GFP_KERNEL);
+	if (!wb_state)
+		return NULL;
+
+	__drm_atomic_helper_connector_duplicate_state(connector,
+						      &wb_state->base);
+
+	return &wb_state->base;
+}
+
+static enum drm_connector_status
+vkms_connector_detect(struct drm_connector *connector, bool force)
+{
+	return connector_status_connected;
+}
+
 static const struct drm_connector_funcs vkms_connector_funcs = {
+	.reset = vkms_connector_reset,
+	.detect = vkms_connector_detect,
 	.fill_modes = drm_helper_probe_single_connector_modes,
 	.destroy = vkms_connector_destroy,
-	.reset = drm_atomic_helper_connector_reset,
-	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
+	.atomic_duplicate_state = vkms_connector_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 };
 
@@ -42,12 +86,35 @@ static const struct drm_connector_helper_funcs vkms_conn_helper_funcs = {
 	.get_modes    = vkms_conn_get_modes,
 };
 
+static int vkms_encoder_atomic_check(struct drm_encoder *encoder,
+				     struct drm_crtc_state *crtc_state,
+				     struct drm_connector_state *conn_state)
+{
+	struct drm_framebuffer *fb;
+
+	if (!conn_state->writeback_job || !conn_state->writeback_job->fb)
+		return 0;
+
+	fb = conn_state->writeback_job->fb;
+	if (fb->width != crtc_state->mode.hdisplay ||
+	    fb->height != crtc_state->mode.vdisplay) {
+		DRM_DEBUG_KMS("Invalid framebuffer size %ux%u\n",
+			      fb->width, fb->height);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static const struct drm_encoder_helper_funcs vkms_encoder_helper_funcs = {
+	.atomic_check = vkms_encoder_atomic_check,
+};
+
 int vkms_output_init(struct vkms_device *vkmsdev)
 {
 	struct vkms_output *output = &vkmsdev->output;
 	struct drm_device *dev = &vkmsdev->drm;
-	struct drm_connector *connector = &output->connector;
-	struct drm_encoder *encoder = &output->encoder;
+	struct drm_writeback_connector *connector = &output->connector;
 	struct drm_crtc *crtc = &output->crtc;
 	struct drm_plane *primary, *cursor = NULL;
 	int ret;
@@ -68,47 +135,29 @@ int vkms_output_init(struct vkms_device *vkmsdev)
 	if (ret)
 		goto err_crtc;
 
-	ret = drm_connector_init(dev, connector, &vkms_connector_funcs,
-				 DRM_MODE_CONNECTOR_VIRTUAL);
+	ret = drm_writeback_connector_init(dev, connector,
+					   &vkms_connector_funcs,
+					   &vkms_encoder_helper_funcs,
+					   vkms_formats, 1);
 	if (ret) {
 		DRM_ERROR("Failed to init connector\n");
 		goto err_connector;
 	}
 
-	drm_connector_helper_add(connector, &vkms_conn_helper_funcs);
+	drm_connector_helper_add(&connector->base, &vkms_conn_helper_funcs);
 
-	ret = drm_connector_register(connector);
+	ret = drm_connector_register(&connector->base);
 	if (ret) {
 		DRM_ERROR("Failed to register connector\n");
 		goto err_connector_register;
 	}
 
-	ret = drm_encoder_init(dev, encoder, &vkms_encoder_funcs,
-			       DRM_MODE_ENCODER_VIRTUAL, NULL);
-	if (ret) {
-		DRM_ERROR("Failed to init encoder\n");
-		goto err_encoder;
-	}
-	encoder->possible_crtcs = 1;
-
-	ret = drm_connector_attach_encoder(connector, encoder);
-	if (ret) {
-		DRM_ERROR("Failed to attach connector to encoder\n");
-		goto err_attach;
-	}
-
 	drm_mode_config_reset(dev);
 
 	return 0;
 
-err_attach:
-	drm_encoder_cleanup(encoder);
-
-err_encoder:
-	drm_connector_unregister(connector);
-
 err_connector_register:
-	drm_connector_cleanup(connector);
+	drm_connector_cleanup(&connector->base);
 
 err_connector:
 	drm_crtc_cleanup(crtc);
-- 
2.19.1


-- 
Rodrigo Siqueira
https://siqueira.tech
https://twitter.com/siqueirajordao
Graduate Student
Department of Computer Science
University of São Paulo
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