On Mon, Apr 19, 2021 at 07:01:00AM +0800, Kevin Tang wrote:
> Maxime Ripard <maxime@xxxxxxxxxx> 于2021年4月15日周四 下午5:03写道：
> > On Thu, Apr 15, 2021 at 08:18:52AM +0800, Kevin Tang wrote:
> > > Maxime Ripard <maxime@xxxxxxxxxx> 于2021年3月24日周三 下午7:10写道：
> > > > > +static struct sprd_dpu *sprd_crtc_init(struct drm_device *drm,
> > > > > + struct drm_plane *primary)
> > > > > +{
> > > > > + struct device_node *port;
> > > > > + struct sprd_dpu *dpu;
> > > > > +
> > > > > + /*
> > > > > + * set crtc port so that drm_of_find_possible_crtcs call works
> > > > > + */
> > > > > + port = of_parse_phandle(drm->dev->of_node, "ports", 0);
> > > > > + if (!port) {
> > > > > + drm_err(drm, "find 'ports' phandle of %s failed\n",
> > > > > + drm->dev->of_node->full_name);
> > > > > + return ERR_PTR(-EINVAL);
> > > > > + }
> > > > > + of_node_put(port);
> > > >
> > > > The YAML binding should already make sure that your binding is sane, and
> > > > if you still get a DT that doesn't follow it, you have a whole lot of
> > > > other issues than whether ports is there :)
> > > >
> > > > > + dpu = drmm_crtc_alloc_with_planes(drm, struct sprd_dpu, base,
> > > > > + primary, NULL,
> > > > > + &sprd_crtc_funcs, NULL);
> > > > > + if (IS_ERR(dpu)) {
> > > > > + drm_err(drm, "failed to init crtc.\n");
> > > > > + return dpu;
> > > > > + }
> > > > > +
> > > > > + dpu->base.port = port;
> > > >
> > > > But you're still referencing it here, while you called of_node_put on it
> > > > already? You should only call it once you're done with it.
> > >
> > > of_node_put should be called after done with it, this maybe indeed be a bug.
> > > i will fix it.
> > > >
> > > >
> > > > I'm not really sure why you would need drm_of_find_possible_crtcs to
> > > > work then if you don't follow the OF-Graph bindings.
> > >
> > > it scan all endports of encoder, if a matching crtc is found by
> > > OF-Graph bindings
> > > and then genarate the crtc mask, here is description:
> > > 41 /**
> > > 42 * drm_of_find_possible_crtcs - find the possible CRTCs for an encoder port
> > > 43 * @dev: DRM device
> > > 44 * @port: encoder port to scan for endpoints
> > > 45 *
> > > 46 * Scan all endpoints attached to a port, locate their attached CRTCs,
> > > 47 * and generate the DRM mask of CRTCs which may be attached to this
> > > 48 * encoder.
> > > 49 *
> > > if we don't follow the OF-Graph bindings, crtc can't attched to encoder.
> >
> > Yeah, what I'm actually confused about is why you would need the
> > of_parse_phandle call. You usually call drm_of_find_possible_crtcs with
> > the encoder device node, so from your MIPI-DSI driver in your case, and
> > with it's device->of_node pointer and it should work perfectly fine?
> I still confused about use drm_of_find_possible_crtcs to bind crtc and
> encoder, the port of drm_crtc, default is null?
>
> 709 /**
> 710 * struct drm_crtc - central CRTC control structure
> 711 * @dev: parent DRM device
> 712 * @port: OF node used by drm_of_find_possible_crtcs()
> -----------------------------------------------------------------------------------------------------
> 25 static uint32_t drm_crtc_port_mask(struct drm_device *dev,
> 26 struct device_node *port)
> 27 {
> 28 unsigned int index = 0;
> 29 struct drm_crtc *tmp;
> 30
> 31 drm_for_each_crtc(tmp, dev) {
> 32 if (tmp->port == port)
> 33 return 1 << index;
> 34
> 35 index++;
> 36 }
> 37
> 38 return 0;
> 39 }
>
> I did not see any place to initialize the port of drm_crtc in the drm
> framework, if not setup it.
> it looks like the port of drm_crtc is undefined.
>
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/rockchip/rockchip_drm_vop.c#L1851
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/tilcdc/tilcdc_crtc.c#L1051
Yeah, you need to initialize it for drm_of_find_possible_crtcs to work,
but my point was that you shouldn't do it through of_parse_phandle, just
put the output of_graph_get_port_by_id like you found in those drivers.
Maxime
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