Re: [PATCH V2 5/5] drm/vkms: Add support for writeback

[Rodrigo Siqueira]

On Tue, Jun 18, 2019 at 6:34 AM Daniel Vetter <daniel@xxxxxxxx> wrote:
>
> On Mon, Jun 17, 2019 at 11:45:55PM -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.
> >
> > Change in V2:
> > - Rework signal completion (Brian)
> > - Integrates writeback with active_planes (Daniel)
> > - Compose cursor (Daniel)
>
> Not quite what I had in mind ... my idea was to reuse the crc worker
> (hence renaming all that stuff to vkms_composer). The problem here is that
> now we have the blend/compose code duplicated, at least parts of it. Plus
> if you enable both crc and writeback, then we compose 2x, which is a bit
> too much.
>
> Rough sketch of an implementation:
>
> - add writeback_pending, like we have crc_pending already. Difference is
>   that writeback is one-shot, i.e. set it in atomic_check somewhere, clear
>   it in the crc_worker (well, composer_worker now). vblank hrtimer will
>   not re-enable that one (unlike crc_pending).
>
> - in the crc worker, if writeback_pending is set, then compose everything
>   into the writeback buffer instead of into our private crc buffer. Except
>   that we use different memory, crc computation will be done exactly the
>   same. For subsequent frames with the same crtc_state we will again use
>   the normal crc buffer to compose & compute the crc.
>
> The benefit here is that we'll only have one place in vkms that does
> composing, so if we add lots more features in the future, it'll be much
> easier to maintain. Also since this guarantees that the crc will match
> exactly what we've written back, we can use the crc to help validate our
> writeback code.

Thanks for your review and comments, I think that I understood all of
them. Iâll prepare a V3.

> Cheers, Daniel
>
> >
> > Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx>
> > ---
> >  drivers/gpu/drm/vkms/Makefile         |   3 +-
> >  drivers/gpu/drm/vkms/vkms_drv.c       |   7 ++
> >  drivers/gpu/drm/vkms/vkms_drv.h       |   6 +
> >  drivers/gpu/drm/vkms/vkms_output.c    |   6 +
> >  drivers/gpu/drm/vkms/vkms_writeback.c | 166 ++++++++++++++++++++++++++
> >  5 files changed, 187 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 b4c040854bd6..091e6fa643d1 100644
> > --- a/drivers/gpu/drm/vkms/Makefile
> > +++ b/drivers/gpu/drm/vkms/Makefile
> > @@ -6,6 +6,7 @@ vkms-y := \
> >       vkms_crtc.o \
> >       vkms_gem.o \
> >       vkms_composer.o \
> > -     vkms_crc.o
> > +     vkms_crc.o \
> > +     vkms_writeback.o
> >
> >  obj-$(CONFIG_DRM_VKMS) += vkms.o
> > diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> > index 966b3d653189..d870779abf9d 100644
> > --- a/drivers/gpu/drm/vkms/vkms_drv.c
> > +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> > @@ -30,6 +30,10 @@ bool enable_cursor;
> >  module_param_named(enable_cursor, enable_cursor, bool, 0444);
> >  MODULE_PARM_DESC(enable_cursor, "Enable/Disable cursor support");
> >
> > +bool enable_writeback;
> > +module_param_named(enable_writeback, enable_writeback, bool, 0444);
> > +MODULE_PARM_DESC(enable_writeback, "Enable/Disable writeback connector");
> > +
> >  static const struct file_operations vkms_driver_fops = {
> >       .owner          = THIS_MODULE,
> >       .open           = drm_open,
> > @@ -158,6 +162,9 @@ static int __init vkms_init(void)
> >               goto out_fini;
> >       }
> >
> > +     if (enable_writeback)
> > +             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 ad63dbe5e994..bf3fa737b3d7 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
> > @@ -19,6 +20,7 @@
> >  #define YRES_MAX  8192
> >
> >  extern bool enable_cursor;
> > +extern bool enable_writeback;
> >
> >  struct vkms_data {
> >       struct drm_framebuffer fb;
> > @@ -63,6 +65,7 @@ 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;
> > @@ -143,4 +146,7 @@ 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 fb1941a6522c..3b093ae8f373 100644
> > --- a/drivers/gpu/drm/vkms/vkms_output.c
> > +++ b/drivers/gpu/drm/vkms/vkms_output.c
> > @@ -84,6 +84,12 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
> >               goto err_attach;
> >       }
> >
> > +     if (enable_writeback) {
> > +             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..56632eb393cb
> > --- /dev/null
> > +++ b/drivers/gpu/drm/vkms/vkms_writeback.c
> > @@ -0,0 +1,166 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +
> > +#include "vkms_drv.h"
> > +#include "vkms_composer.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 != 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 vkms_crtc_state *crtc_state = output->crc_state;
> > +     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_data *primary_data = NULL;
> > +     struct vkms_data *cursor_data = NULL;
> > +     struct drm_framebuffer *fb = NULL;
> > +     struct vkms_gem_object *vkms_obj;
> > +     struct drm_gem_object *gem_obj;
> > +
> > +     if (!conn_state)
> > +             return;
> > +
> > +     if (!conn_state->writeback_job || !conn_state->writeback_job->fb) {
> > +             DRM_DEBUG_DRIVER("Disable writeback\n");
> > +             return;
> > +     }
> > +
> > +     if (crtc_state->num_active_planes >= 1)
> > +             primary_data = crtc_state->active_planes[0]->data;
> > +
> > +     if (crtc_state->num_active_planes == 2)
> > +             cursor_data = crtc_state->active_planes[1]->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;
> > +
> > +     drm_writeback_queue_job(wb_conn, state);
> > +
> > +     memcpy(priv_data, vkms_obj->vaddr, vkms_obj->gem.size);
> > +     if (cursor_data)
> > +             compose_cursor(cursor_data, primary_data, priv_data);
> > +
> > +     drm_writeback_signal_completion(wb_conn, 0);
> > +}
> > +
> > +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_wb_formats,
> > +                                         ARRAY_SIZE(vkms_wb_formats));
> > +}
> > +
> > --
> > 2.21.0
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch



-- 

Rodrigo Siqueira
https://siqueira.tech