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Subject: Re: [PATCH v13 6/9] dw-hdmi/ingenic-dw-hdmi: repair interworking with
 hdmi-connector
From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <E6E17R.ND5XW1IG4SYA@crapouillou.net>
Date:   Wed, 9 Feb 2022 14:51:17 +0100
Cc:     Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Kees Cook <keescook@chromium.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Robert Foss <robert.foss@linaro.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Harry Wentland <harry.wentland@amd.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Maxime Ripard <maxime@cerno.tech>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Paul Boddie <paul@boddie.org.uk>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
        devicetree@vger.kernel.org, linux-mips@vger.kernel.org,
        linux-kernel@vger.kernel.org, letux-kernel@openphoenux.org,
        Jonas Karlman <jonas@kwiboo.se>,
        dri-devel@lists.freedesktop.org
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Message-Id: <987D3DDA-FA93-4EDB-ABCB-6973DB7FD943@goldelico.com>
References: <cover.1643819482.git.hns@goldelico.com>
 <866f84621974992f4831bd471ae5a53414de9255.1643819482.git.hns@goldelico.com>
 <E6E17R.ND5XW1IG4SYA@crapouillou.net>
To:     Paul Cercueil <paul@crapouillou.net>
Precedence: bulk

Hi Paul,

> Am 09.02.2022 um 13:18 schrieb Paul Cercueil <paul@crapouillou.net>:
>=20
> Hi Nikolaus,
>=20
> Le mer., f=C3=A9vr. 2 2022 at 17:31:20 +0100, H. Nikolaus Schaller =
<hns@goldelico.com> a =C3=A9crit :
>> Commit 7cd70656d1285b ("drm/bridge: display-connector: implement bus =
fmts callbacks")
>> introduced a new mechanism to negotiate bus formats between hdmi =
connector
>> and the synopsys hdmi driver inside the jz4780.
>> By this, the dw-hdmi is no longer the only bridge and sets up a list
>> of formats in dw_hdmi_bridge_atomic_get_output_bus_fmts().
>> This includes MEDIA_BUS_FMT_UYVY8_1X16 which is chosen for the jz4780 =
but only
>> produces a black screen.
>> This fix is based on the observation that max_bpc =3D 0 when running =
this
>> function while info->bpc =3D 8. Since the formats checks before this =
always test
>> for max_bpc >=3D info->pbc indirectly my assumption is that we must =
check it
>> here as well.
>=20
> This fix looks really strange to me, so I'll let the DRM experts =
comment.

Well, yes. We should maybe look for comments by the synopsys/dw-hdmi =
specialists.

>=20
> It would still be better to move the patch before the introduction of =
dw-ingenic-hdmi.c, so that once this one is introduced, everything =
works. This also enables bisectability.

Ok, good.

BR and thanks,
Nikolaus

>=20
> Cheers,
> -Paul
>=20
>=20
>> Adding the proposed patch makes the CI20/jz4780 panel work again in
>> MEDIA_BUS_FMT_RGB888_1X24 mode.
>> Fixes: 7cd70656d1285b ("drm/bridge: display-connector: implement bus =
fmts callbacks")
>> Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
>> ---
>> drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c =
b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> index 52e7cd2e020d3..34703a15ee4ff 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> @@ -2620,10 +2620,10 @@ static u32 =
*dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
>> 		output_fmts[i++] =3D MEDIA_BUS_FMT_RGB101010_1X30;
>> 	}
>> -	if (info->color_formats & DRM_COLOR_FORMAT_YCRCB422)
>> +	if (max_bpc >=3D info->bpc && info->color_formats & =
DRM_COLOR_FORMAT_YCRCB422)
>> 		output_fmts[i++] =3D MEDIA_BUS_FMT_UYVY8_1X16;
>> -	if (info->color_formats & DRM_COLOR_FORMAT_YCRCB444)
>> +	if (max_bpc >=3D info->bpc && info->color_formats & =
DRM_COLOR_FORMAT_YCRCB444)
>> 		output_fmts[i++] =3D MEDIA_BUS_FMT_YUV8_1X24;
>> 	/* Default 8bit RGB fallback */
>> --
>> 2.33.0
>=20
>=20