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Date:   Mon, 13 Apr 2020 13:25:13 +0200
From:   Paul Cercueil <paul@crapouillou.net>
Subject: Re: DRM interaction problems on Ingenic CI20 / jz4780 with dw-hdmi
 and ingenic-drm
To:     "H. Nikolaus Schaller" <hns@goldelico.com>
Cc:     Dave Airlie <airlied@linux.ie>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Andy Yan <andy.yan@rock-chips.com>,
        Yakir Yang <ykk@rock-chips.com>,
        Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>,
        Paul Boddie <paul@boddie.org.uk>, linux-mips@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        MIPS Creator CI20 Development 
        <mips-creator-ci20-dev@googlegroups.com>
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Hi Nikolaus,


Le sam. 11 avril 2020 =E0 16:14, H. Nikolaus Schaller=20
<hns@goldelico.com> a =E9crit :
> Hi,
> we (Paul Boddie and me) are working to get HDMI functional on the
> Ingenic CI20 board with jz4780 SoC which uses a specialization of
> the dw-hdmi driver.
>=20
>=20
> So far we have identified two issues.
>=20
> The first is that HPD interrupts are not properly processed.
>=20
> drm_helper_hpd_irq_event() is called by HPD events but
> dev->mode_config.poll_enabled is false.
>=20
> Therefore the interrupt is ignored and nothing happens.
>=20
> Now I wonder about the logic behind checking for poll_enabled.
> I understand that a driver can do either polling or irq or both.
>=20
> Therefore handling the irq_event shouldn't be disabled by poll_enabled
> being false. Otherwise we can only do: nothing, polling, polling+irq
> but not irq alone.
>=20
> The jz4780 hdmi subsystem (drm/bridge/dw-hdmi.c) uses
>=20
> 	connector->polled =3D DRM_CONNECTOR_POLL_HPD;
>=20
> but shouldn't this enable polling? Note that there seems to be
> no (direct) call to drm_kms_helper_poll_init().
>=20
> If we set dev->mode_config.poll_enabled =3D true in
> drm_helper_hpd_irq_event() things start to work.
>=20
> Please can you clarify what would be best practise here to
> get HPD event handling working.
>=20
>=20
> The other issue is in dw-hdmi.c:
>=20
> We found out that ingenic_drm_encoder_atomic_check() fails because
>=20
> info->num_bus_formats =3D=3D 0
>=20
> and not 1. This blocks further initialization.
>=20
> The reason seems to be that dw_hdmi_bridge_attach() does not call
> drm_display_info_set_bus_formats() with a proper format like
> other drivers (e.g. drm/bridge/ti-tfp410.c) are doing.
>=20
> We have patched to set a single bus format MEDIA_BUS_FMT_RGB888_1X24
> and then DRM setup seems to work (although we still have no valid
> HDMI signal but that is likely something else).
>=20
> Please can you explain how setting the bus format should be fixed
> in dw-hdmi.c.
>=20
> If these questions should be forwarded to other specialists, please
> do so.

It should be sent to the DRI mailing list, you missed the most=20
important one.

-Paul

>=20
> BR and thanks,
> Nikolaus Schaller