Message-ID: <20190416124307.GQ15144@e110455-lin.cambridge.arm.com>
Date:   Tue, 16 Apr 2019 13:43:07 +0100
From:   Liviu Dudau <Liviu.Dudau@....com>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     "james qian wang (Arm Technology China)" <james.qian.wang@....com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "maxime.ripard@...tlin.com" <maxime.ripard@...tlin.com>,
        nd <nd@....com>, "sean@...rly.run" <sean@...rly.run>,
        Ben Davis <Ben.Davis@....com>
Subject: Re: [v2,1/2] drm: Add writeback_w,h properties

On Tue, Apr 16, 2019 at 11:55:34AM +0200, Daniel Vetter wrote:
> On Tue, Apr 16, 2019 at 11:17 AM Liviu Dudau <Liviu.Dudau@....com> wrote:
> >
> > On Tue, Apr 16, 2019 at 09:34:20AM +0200, Daniel Vetter wrote:
> > > On Mon, Apr 15, 2019 at 10:20:45AM +0100, Liviu Dudau wrote:
> > > > On Mon, Apr 15, 2019 at 08:59:30AM +0100, james qian wang (Arm Technology China) wrote:
> > > > > On Fri, Apr 12, 2019 at 02:08:28PM +0000, Ben Davis wrote:
> > > > > > Add new properties to specify width and height for writeback.
> > > > > >
> > > > > > Signed-off-by: Ben Davis <ben.davis@....com>
> > > > > > ---
> > > > > >  drivers/gpu/drm/drm_atomic_uapi.c |  8 ++++++++
> > > > > >  drivers/gpu/drm/drm_writeback.c   | 28 ++++++++++++++++++++++++++++
> > > > > >  include/drm/drm_connector.h       |  4 ++++
> > > > > >  include/drm/drm_mode_config.h     | 10 ++++++++++
> > > > > >  4 files changed, 50 insertions(+)
> > > > > >
> > > > > > --
> > > > > > 2.7.4
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> > > > > > index d520a04..1f68dce 100644
> > > > > > --- a/drivers/gpu/drm/drm_atomic_uapi.c
> > > > > > +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> > > > > > @@ -765,6 +765,10 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
> > > > > >                         return -EINVAL;
> > > > > >                 }
> > > > > >                 state->content_protection = val;
> > > > > > +       } else if (property == config->prop_writeback_w) {
> > > > > > +               state->writeback_w = val;
> > > > > > +       } else if (property == config->prop_writeback_h) {
> > > > > > +               state->writeback_h = val;
> > > > > >         } else if (property == config->writeback_fb_id_property) {
> > > > > >                 struct drm_framebuffer *fb = drm_framebuffer_lookup(dev, NULL, val);
> > > > > >                 int ret = drm_atomic_set_writeback_fb_for_connector(state, fb);
> > > > > > @@ -837,6 +841,10 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
> > > > > >                 *val = state->scaling_mode;
> > > > > >         } else if (property == connector->content_protection_property) {
> > > > > >                 *val = state->content_protection;
> > > > > > +       } else if (property == config->prop_writeback_w) {
> > > > > > +               *val = state->writeback_w;
> > > > > > +       } else if (property == config->prop_writeback_h) {
> > > > > > +               *val = state->writeback_h;
> > > > > >         } else if (property == config->writeback_fb_id_property) {
> > > > > >                 /* Writeback framebuffer is one-shot, write and forget */
> > > > > >                 *val = 0;
> > > > > > diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
> > > > > > index c20e6fe..3d0453e 100644
> > > > > > --- a/drivers/gpu/drm/drm_writeback.c
> > > > > > +++ b/drivers/gpu/drm/drm_writeback.c
> > > > > > @@ -74,6 +74,12 @@
> > > > > >   *     applications making use of writeback connectors *always* retrieve an
> > > > > >   *     out-fence for the commit and use it appropriately.
> > > > > >   *     From userspace, this property will always read as zero.
> > > > > > + *
> > > > > > + *  "WRITEBACK_W":
> > > > > > + *     The width of the writeback buffer to write back. 0 acts as default.
> > > > > > + *
> > > > > > + *  "WRITEBACK_H":
> > > > > > + *     The height of the writeback buffer to write back. 0 acts as default.
> > > > > >   */
> > > > > >
> > > > > >  #define fence_to_wb_connector(x) container_of(x->lock, \
> > > > > > @@ -141,6 +147,22 @@ static int create_writeback_properties(struct drm_device *dev)
> > > > > >                 dev->mode_config.writeback_out_fence_ptr_property = prop;
> > > > > >         }
> > > > > >
> > > > > > +       if (!dev->mode_config.prop_writeback_w) {
> > > > > > +               prop = drm_property_create_range(dev, DRM_MODE_PROP_ATOMIC,
> > > > > > +                                                "WRITEBACK_W", 1, UINT_MAX);
> > > > > > +               if (!prop)
> > > > > > +                       return -ENOMEM;
> > > > > > +               dev->mode_config.prop_writeback_w = prop;
> > > > > > +       }
> > > > > > +
> > > > > > +       if (!dev->mode_config.prop_writeback_h) {
> > > > > > +               prop = drm_property_create_range(dev, DRM_MODE_PROP_ATOMIC,
> > > > > > +                                                "WRITEBACK_H", 1, UINT_MAX);
> > > > > > +               if (!prop)
> > > > > > +                       return -ENOMEM;
> > > > > > +               dev->mode_config.prop_writeback_h = prop;
> > > > > > +       }
> > > > > > +
> > > > > >         return 0;
> > > > > >  }
> > > > > >
> > > > > > @@ -225,6 +247,12 @@ int drm_writeback_connector_init(struct drm_device *dev,
> > > > > >         drm_object_attach_property(&connector->base,
> > > > > >                                    config->writeback_pixel_formats_property,
> > > > > >                                    blob->base.id);
> > > > > > +
> > > > > > +       drm_object_attach_property(&connector->base,
> > > > > > +                                  config->prop_writeback_w, 0);
> > > > > > +       drm_object_attach_property(&connector->base,
> > > > > > +                                  config->prop_writeback_h, 0);
> > > > >
> > > > > Hi Ben:
> > > > > Do we real need these two individual properties for specifing the writeback
> > > > > w/h, can we use fb->w/h ?
> > > > > And since these two properties are added as common and standard properties,
> > > > > it influnce all existing write-back implementation which all assumed
> > > > > writeback size as fb->w/h.
> > > >
> > > > The idea of having these additional properties was to maintain backwards
> > > > compatibility (of some sort). If you don't set writeback_w/h then the
> > > > assumption is that they are the same as fb->w/h, but I can see how it's
> > > > going to be confusing to have fb->w/h different from crtc->w/h and
> > > > different from writeback_w/h.
> > >
> > > Since we already have crtc_w/h independent of writeback_fb_w/h, do we need
> > > another set of w/h? Are all the interactions between these tree
> > > well-defined?
> >
> > No, we probably don't need another set of w/h values. As for the
> > interaction, I propose the following:
> >
> > - writeback is only attached to a connector, so the crtc_x/y/w/h are the
> >   "input source" parameters into the writeback. Given that we put in the
> >   writeback the content of the CRTC, I suggest we ignore x,y (consider
> >   them to be always 0 for the writeback output).
> 
> There's no crtc_x/y. 

Bah, sorry about that!

>                       And what I meant with crtc_w/h is
> crtc_state->mode->h/vdisplay. And you can already express scaling with
> that, by setting the plane_state->crtc_x/y/h/w parameters as you wish.

We don't have a plane associated with the writeback, it's a connector
with a framebuffer attached to it. :(

> 
> > - writeback has a framebuffer attached, so we can use the fb->w/h to
> >   determine if we need to do any scaling of the output.
> 
> Hm, not sure we want that. You might want to automatically round
> fb->w/h to whatever (ok right now we don't do that I think anywhere),
> so forcing the output to match the fb->h/w doesn't make sense for me.
> It's also inconsistent with how we treat fb attached to planes (where
> we have the full set of src coordinates).

The writeback will have to fit into that framebuffer, so it can't be
bigger than fb->w/h. Smaller, yes.


> 
> > > Atm I'm assuming that writeback is using crtc_w/h into the fb, at offset
> > > 0, not scaled any further. But the planes themselves can be scaled into
> > > the crtc_w/h window ofc.
> >
> > Our hardware has the ability to also write back one of the planes and
> > scale it during writeback, but we have no way of expressing that in DRM
> > via connectors, so we are going to ignore that case. The supported usecase
> > is for the planes to be scaled into the "composition" area which is the size
> > of the CRTC, and then writeback that to memory, possibly with scaling (we
> > officially only going to support downscaling due to external dependencies
> > on the memory clock that is needed for supporting upscaling).
> 
> Hm, see above, you can already express that:
> - set crtc_state->mode->h/vdisplay to what you want the resulting
> writeback image to be sized at.
> - place the plane however you want using the plane properties within
> that crtc window.

The way we agreed ~2 years ago in the community to implement this was to have
the writeback as a connector that gets the "output" of the CRTC and writes it into
memory rather than on phosphorus. We have not added a plane to that, but
in hindsight we might find it would have been useful.

Best regards,
Liviu


> 
> Cheers, Daniel
> 
> >
> > Liviu
> >
> >
> > >
> > > Iirc the hw supporting writeback thus far needs a dedicated crtc for
> > > writeback, so adding yet another scaling window is not needed?
> > > -Daniel
> > >
> > > > > To compatible with existing writeback support, I suggest to keep to
> > > > > use fb->w/h or add these properties as malidp private.
> > > >
> > > > We don't need to make them malidp private, there is nothing malidp
> > > > specific in them. I'll talk with Ben, we should probably drop this patch
> > > > entirely and just enable malidp scaling when fb->w/h differ from
> > > > crtc->w/h.
> > > >
> > > > Best regards,
> > > > Liviu
> > > >
> > > >
> > > > >
> > > > > Thanks
> > > > > James
> > > > >
> > > > >
> > > > > >         wb_connector->pixel_formats_blob_ptr = blob;
> > > > > >
> > > > > >         return 0;
> > > > > > diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> > > > > > index 8fe22ab..51c4cb2 100644
> > > > > > --- a/include/drm/drm_connector.h
> > > > > > +++ b/include/drm/drm_connector.h
> > > > > > @@ -515,6 +515,10 @@ struct drm_connector_state {
> > > > > >          */
> > > > > >         struct drm_writeback_job *writeback_job;
> > > > > >
> > > > > > +       /** @writeback_w: width of plane to write to wb buffer */
> > > > > > +       /** @writeback_h: height of plane to write to wb buffer */
> > > > > > +       uint32_t writeback_w, writeback_h;
> > > > > > +
> > > > > >         /**
> > > > > >          * @max_requested_bpc: Connector property to limit the maximum bit
> > > > > >          * depth of the pixels.
> > > > > > diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> > > > > > index 7f60e8e..a0c2133 100644
> > > > > > --- a/include/drm/drm_mode_config.h
> > > > > > +++ b/include/drm/drm_mode_config.h
> > > > > > @@ -622,6 +622,16 @@ struct drm_mode_config {
> > > > > >          */
> > > > > >         struct drm_property *prop_crtc_h;
> > > > > >         /**
> > > > > > +        * @prop_writeback_w: Writeback connector property for the plane
> > > > > > +        * destination position in the writeback buffer.
> > > > > > +        */
> > > > > > +       struct drm_property *prop_writeback_w;
> > > > > > +       /**
> > > > > > +        * @prop_writeback_h: Writeback connector property for the plane
> > > > > > +        * destination position in the writeback buffer.
> > > > > > +        */
> > > > > > +       struct drm_property *prop_writeback_h;
> > > > > > +       /**
> > > > > >          * @prop_fb_id: Default atomic plane property to specify the
> > > > > >          * &drm_framebuffer.
> > > > > >          */
> > > > >
> > > > > Pls del this window style line ending
> > > > >
> > > >
> > > > --
> > > > ====================
> > > > | I would like to |
> > > > | fix the world,  |
> > > > | but they're not |
> > > > | giving me the   |
> > > >  \ source code!  /
> > > >   ---------------
> > > >     ¯\_(ツ)_/¯
> > > > _______________________________________________
> > > > dri-devel mailing list
> > > > dri-devel@...ts.freedesktop.org
> > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> > >
> > > --
> > > Daniel Vetter
> > > Software Engineer, Intel Corporation
> > > http://blog.ffwll.ch
> >
> > --
> > ====================
> > | I would like to |
> > | fix the world,  |
> > | but they're not |
> > | giving me the   |
> >  \ source code!  /
> >   ---------------
> >     ¯\_(ツ)_/¯
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@...ts.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

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