Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 21 Apr 2021 12:00:52 +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: <20210421100052.gujzkrafp26e6tcz@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>
 <20210415090312.md6exuuv2y4mblxn@gilmour>
 <CAFPSGXYdA=09xWZJi2oCQsbr3eH1GBgzjD8DRm5=beiKAtx37Q@mail.gmail.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
        protocol="application/pgp-signature"; boundary="kpgrv3m2gbmdl54j"
Content-Disposition: inline
In-Reply-To: <CAFPSGXYdA=09xWZJi2oCQsbr3eH1GBgzjD8DRm5=beiKAtx37Q@mail.gmail.com>
Precedence: bulk


--kpgrv3m2gbmdl54j
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Mon, Apr 19, 2021 at 07:01:00AM +0800, Kevin Tang wrote:
> Maxime Ripard <maxime@cerno.tech> =E4=BA=8E2021=E5=B9=B44=E6=9C=8815=E6=
=97=A5=E5=91=A8=E5=9B=9B =E4=B8=8B=E5=8D=885:03=E5=86=99=E9=81=93=EF=BC=9A
> > 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 wo=
rks
> > > > > +      */
> > > > > +     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, b=
ase,
> > > > > +                                     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.
> > >
> > >  of_node_put should be called after done with it, this maybe indeed b=
e 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 en=
coder 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 C=
RTCs,
> > > 47   * and generate the DRM mask of CRTCs which may be attached to th=
is
> > > 48   * encoder.
> > > 49   *
> > > if we don't follow the OF-Graph bindings, crtc can't attched to encod=
er.
> >
> > 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?
>=20
> 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 =3D 0;
> 29   struct drm_crtc *tmp;
> 30
> 31   drm_for_each_crtc(tmp, dev) {
> 32   if (tmp->port =3D=3D port)
> 33   return 1 << index;
> 34
> 35   index++;
> 36   }
> 37
> 38   return 0;
> 39  }
>=20
> 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.
>=20
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/rockchip/r=
ockchip_drm_vop.c#L1851
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/tilcdc/til=
cdc_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

--kpgrv3m2gbmdl54j
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iHUEABYIAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCYH/31AAKCRDj7w1vZxhR
xfYbAQCyx/frCmI48iF2v9KLvwRkV6q7XhdIGq6JZ8So9sDZdwEAg7fNpob0hObc
+1Speo1tpFxjtmM3FtNHpH8nYvYk4ww=
=LDrh
-----END PGP SIGNATURE-----

--kpgrv3m2gbmdl54j--