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SubjectRe: [PATCH 2/2] drm/vkms: Add support for writeback
Date
Hi Rodrigo,

On Thu, Jun 06, 2019 at 07:41:01PM -0300, Rodrigo Siqueira wrote:
> 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.
>
> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> ---
> drivers/gpu/drm/vkms/Makefile | 9 +-
> drivers/gpu/drm/vkms/vkms_crtc.c | 5 +
> drivers/gpu/drm/vkms/vkms_drv.c | 10 ++
> drivers/gpu/drm/vkms/vkms_drv.h | 12 ++
> drivers/gpu/drm/vkms/vkms_output.c | 6 +
> drivers/gpu/drm/vkms/vkms_writeback.c | 165 ++++++++++++++++++++++++++
> 6 files changed, 206 insertions(+), 1 deletion(-)
> create mode 100644 drivers/gpu/drm/vkms/vkms_writeback.c
>
> diff --git a/drivers/gpu/drm/vkms/Makefile b/drivers/gpu/drm/vkms/Makefile
> index 89f09bec7b23..90eb7acd618d 100644
> --- a/drivers/gpu/drm/vkms/Makefile
> +++ b/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_crc.o
> +vkms-y := \
> + vkms_drv.o \
> + vkms_plane.o \
> + vkms_output.o \
> + vkms_crtc.o \
> + vkms_gem.o \
> + vkms_crc.o \
> + vkms_writeback.o
>
> obj-$(CONFIG_DRM_VKMS) += vkms.o
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> index 1bbe099b7db8..ce797e265b1b 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -23,6 +23,11 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
> if (!ret)
> DRM_ERROR("vkms failure on handling vblank");
>
> + if (output->writeback_status == WB_START) {
> + drm_writeback_signal_completion(&output->wb_connector, 0);
> + output->writeback_status = WB_STOP;
> + }
> +
> if (state && output->crc_enabled) {
> u64 frame = drm_crtc_accurate_vblank_count(crtc);
>
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> index 92296bd8f623..d5917d5a45e3 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.c
> +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> @@ -29,6 +29,10 @@ bool enable_cursor;
> module_param_named(enable_cursor, enable_cursor, bool, 0444);
> MODULE_PARM_DESC(enable_cursor, "Enable/Disable cursor support");
>
> +int enable_writeback;
> +module_param_named(enable_writeback, enable_writeback, int, 0444);
> +MODULE_PARM_DESC(enable_writeback, "Enable/Disable writeback connector");
> +
> static const struct file_operations vkms_driver_fops = {
> .owner = THIS_MODULE,
> .open = drm_open,
> @@ -123,6 +127,12 @@ static int __init vkms_init(void)
> goto out_fini;
> }
>
> + vkms_device->output.writeback_status = WB_DISABLED;
> + if (enable_writeback) {
> + vkms_device->output.writeback_status = WB_STOP;
> + DRM_INFO("Writeback connector enabled");
> + }
> +
> ret = vkms_modeset_init(vkms_device);
> if (ret)
> goto out_fini;
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index e81073dea154..ca1f9ee63ec8 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -7,6 +7,7 @@
> #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
> @@ -60,14 +61,22 @@ struct vkms_crtc_state {
> u64 frame_end;
> };
>
> +enum wb_status {
> + WB_DISABLED,
> + WB_START,
> + WB_STOP,
> +};
> +
> 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;
> bool crc_enabled;
> + enum wb_status writeback_status;
> /* ordered wq for crc_work */
> struct workqueue_struct *crc_workq;
> /* protects concurrent access to crc_data */
> @@ -141,4 +150,7 @@ int vkms_verify_crc_source(struct drm_crtc *crtc, const char *source_name,
> size_t *values_cnt);
> void vkms_crc_work_handle(struct work_struct *work);
>
> +/* Writeback */
> +int enable_writeback_connector(struct vkms_device *vkmsdev);
> +
> #endif /* _VKMS_DRV_H_ */
> diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
> index 1442b447c707..1fc1d4e9585c 100644
> --- a/drivers/gpu/drm/vkms/vkms_output.c
> +++ b/drivers/gpu/drm/vkms/vkms_output.c
> @@ -91,6 +91,12 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
> goto err_attach;
> }
>
> + if (vkmsdev->output.writeback_status != WB_DISABLED) {
> + ret = enable_writeback_connector(vkmsdev);
> + if (ret)
> + DRM_ERROR("Failed to init writeback connector\n");
> + }
> +
> drm_mode_config_reset(dev);
>
> return 0;
> diff --git a/drivers/gpu/drm/vkms/vkms_writeback.c b/drivers/gpu/drm/vkms/vkms_writeback.c
> new file mode 100644
> index 000000000000..f7b962ae5646
> --- /dev/null
> +++ b/drivers/gpu/drm/vkms/vkms_writeback.c
> @@ -0,0 +1,165 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +
> +#include "vkms_drv.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 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 != DRM_FORMAT_XRGB8888) {
> + 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;
> +
> + if (!job->fb)
> + return;
> +
> + gem_obj = drm_gem_fb_get_obj(job->fb, 0);
> + vkms_gem_vunmap(gem_obj);
> +}
> +
> +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;
> + void *priv_data = conn_state->writeback_job->priv;
> + struct vkms_crc_data *primary_data = NULL;
> + struct drm_framebuffer *fb = NULL;
> + struct vkms_gem_object *vkms_obj;
> + struct drm_gem_object *gem_obj;
> + struct drm_plane *plane;
> +
> + if (!conn_state)
> + return;
> +
> + if (!conn_state->writeback_job || !conn_state->writeback_job->fb) {
> + output->writeback_status = WB_STOP;
> + DRM_DEBUG_DRIVER("Disable writeback\n");
> + return;
> + }
> +
> + drm_for_each_plane(plane, &vkmsdev->drm) {
> + struct vkms_plane_state *vplane_state;
> + struct vkms_crc_data *plane_data;
> +
> + vplane_state = to_vkms_plane_state(plane->state);
> + plane_data = vplane_state->crc_data;
> +
> + if (drm_framebuffer_read_refcount(&plane_data->fb) == 0)
> + continue;

It's not really specific to this patch, but this looks kinda
weird to me. You've got a copy of the fb struct in plane_data?

It seems like that would break a bunch of refcounting if nothing else.

Can't you use plane->state->fb directly, and just check if it's NULL?

> +
> + if (plane->type == DRM_PLANE_TYPE_PRIMARY)
> + primary_data = plane_data;
> + }
> +
> + if (!primary_data)
> + return;
> +
> + fb = &primary_data->fb;
> + gem_obj = drm_gem_fb_get_obj(fb, 0);
> + vkms_obj = drm_gem_to_vkms_gem(gem_obj);
> +
> + if (!vkms_obj->vaddr || !priv_data)
> + return;
> +
> + memcpy(priv_data, vkms_obj->vaddr, vkms_obj->gem.size);
> + drm_writeback_queue_job(wb_conn, state);
> + output->writeback_status = WB_START;

You probably don't need the deferred completion signaling. I'd expect
this to work OK (and it matches the API semantics):

drm_writeback_queue_job(wb_conn, state);
memcpy(priv_data, vkms_obj->vaddr, vkms_obj->gem.size);
drm_writeback_signal_completion(wb_conn, 0);


Cheers,
-Brian

> +}
> +
> +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 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_formats,
> + ARRAY_SIZE(vkms_formats));
> +}
> +
> --
> 2.21.0


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