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Date:   Thu, 15 Apr 2021 11:03:12 +0200
From:   Maxime Ripard <maxime@cerno.tech>
To:     Kevin Tang <kevin3.tang@gmail.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Orson Zhai <orsonzhai@gmail.com>,
        Chunyan Zhang <zhang.lyra@gmail.com>,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
        ML dri-devel <dri-devel@lists.freedesktop.org>,
        devicetree@vger.kernel.org
Subject: Re: [PATCH v4 4/6] drm/sprd: add Unisoc's drm display controller
 driver
Message-ID: <20210415090312.md6exuuv2y4mblxn@gilmour>
References: <20210222132822.7830-1-kevin3.tang@gmail.com>
 <20210222132822.7830-5-kevin3.tang@gmail.com>
 <20210324111019.og6d3w47swjim2mq@gilmour>
 <CAFPSGXYZPoM45vF_HcjMBcO_Ek-UJZw7F+Q0Of-gWZxvVaPQjg@mail.gmail.com>
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Hi,

On Thu, Apr 15, 2021 at 08:18:52AM +0800, Kevin Tang wrote:
> Maxime Ripard <maxime@cerno.tech> =E4=BA=8E2021=E5=B9=B43=E6=9C=8824=E6=
=97=A5=E5=91=A8=E4=B8=89 =E4=B8=8B=E5=8D=887:10=E5=86=99=E9=81=93=EF=BC=9A
> > > +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 =3D 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 =3D 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 =3D 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.
>=20
>  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.
>=20
> 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 encode=
r 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?

Maxime

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