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Subject: Re: [PATCH v15 4/7] drm/bridge: dw-hdmi: repair interworking with
 hdmi-connector for jz4780
From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <9c6f5c0b-5879-736f-344f-dfa12a0d7937@baylibre.com>
Date:   Sat, 26 Feb 2022 18:12:34 +0100
Cc:     Andrzej Hajda <andrzej.hajda@intel.com>,
        Robert Foss <robert.foss@linaro.org>,
        Paul Boddie <paul@boddie.org.uk>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Paul Cercueil <paul@crapouillou.net>,
        Maxime Ripard <maxime@cerno.tech>,
        Harry Wentland <harry.wentland@amd.com>,
        Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
        letux-kernel@openphoenux.org, linux-mips@vger.kernel.org,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Jonas Karlman <jonas@kwiboo.se>
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Message-Id: <3F01AD9B-EA49-4A34-A421-43E9E6268311@goldelico.com>
References: <cover.1644681054.git.hns@goldelico.com>
 <d4d08582c49ec089095dd0ede4cdf2752f9d1eb8.1644681054.git.hns@goldelico.com>
 <9c6f5c0b-5879-736f-344f-dfa12a0d7937@baylibre.com>
To:     Neil Armstrong <narmstrong@baylibre.com>
Precedence: bulk

Hi Neil,

> Am 21.02.2022 um 09:11 schrieb Neil Armstrong =
<narmstrong@baylibre.com>:
>=20
> Hi,
>=20
> On 12/02/2022 16:50, H. Nikolaus Schaller wrote:
>> 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.
>> 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 b0d8110dd412c..826a055a7a273 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_YCBCR422)
>> +	if (max_bpc >=3D info->bpc && info->color_formats & =
DRM_COLOR_FORMAT_YCBCR422)
>>  		output_fmts[i++] =3D MEDIA_BUS_FMT_UYVY8_1X16;
>>  -	if (info->color_formats & DRM_COLOR_FORMAT_YCBCR444)
>> +	if (max_bpc >=3D info->bpc && info->color_formats & =
DRM_COLOR_FORMAT_YCBCR444)
>>  		output_fmts[i++] =3D MEDIA_BUS_FMT_YUV8_1X24;
>>    	/* Default 8bit RGB fallback */
>=20
> Please do the same for all other cases and change the patch subject to =
something more accurate like:
> "drm/bridge: dw-hdmi: take display info bpc in account for bus formats =
negociation"

thank you very much for this analysis.

In fact my fix was also not correctly doing the right comparisons. The =
rules should have the
same structure as for all cases before, i.e. check for >=3D 8 and then =
handle both color formats.
I have fixed and tested on my CI20 board and updated the description and =
Fixes: tags.

v16 will come now (as part of the jz4780 hdmi series).

BR and thanks,
Nikolaus