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Subject: Re: [PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge
 chain
To:     Marcel Ziswiler <marcel.ziswiler@toradex.com>,
        "robert.foss@linaro.org" <robert.foss@linaro.org>
Cc:     "Laurent.pinchart@ideasonboard.com" 
        <Laurent.pinchart@ideasonboard.com>,
        "kieran.bingham@ideasonboard.com" <kieran.bingham@ideasonboard.com>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "biju.das.jz@bp.renesas.com" <biju.das.jz@bp.renesas.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "jonas@kwiboo.se" <jonas@kwiboo.se>,
        "jernej.skrabec@gmail.com" <jernej.skrabec@gmail.com>,
        "kieran.bingham+renesas@ideasonboard.com" 
        <kieran.bingham+renesas@ideasonboard.com>
References: <20220117141750.1182223-1-narmstrong@baylibre.com>
 <cdc8dd0f08aea5f8a32a6da7ec087c8d48d627f5.camel@toradex.com>
From:   Neil Armstrong <narmstrong@baylibre.com>
Organization: Baylibre
Message-ID: <6558973d-8d16-9e41-44ca-4e8cde5ce049@baylibre.com>
Date:   Tue, 18 Jan 2022 08:16:53 +0100
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Hi,

On 17/01/2022 17:53, Marcel Ziswiler wrote:
> Hi Neil
> 
> Sorry, just some trivial spelling fixes.
> 
> On Mon, 2022-01-17 at 15:17 +0100, Neil Armstrong wrote:
>> When the dw-hdmi bridge is in first place of the bridge chain, this
>> means there is now way
> 
> no way
> 
>> to select an input format of the dw-hdmi HW
>> component.
>>
>> Since introduction of display-connector, negociation
> 
> :%s/negociation/negotiation/g
> 
>> was broken since
>> the dw-hdmi negociation code only worked when the dw-hdmi bridge was
>> in last position of the bridge chain or behind another bridge also
>> supporting input & output format negociation.
>>
>> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
>> was introduced to make negociation work again by making display-connector
>> act as a pass-through concerning input & output format negociation.
>>
>> But in the case were
> 
> where
> 
>> the dw-hdmi was single in the bridge chain, for
>> example on Renesas SoCs, with the disply-connector
> 
> display-connector
> 
>> bridge the dw-hdmi
>> is no more single, breaking output format.
>>
>> Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
>> Bisected-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>> Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>> Fixes: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks").
>> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
>> ---
>>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> index 54d8fdad395f..9f2e1cac0ae2 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> @@ -2551,8 +2551,9 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
>>         if (!output_fmts)
>>                 return NULL;
>>  
>> -       /* If dw-hdmi is the only bridge, avoid negociating with ourselves */
>> -       if (list_is_singular(&bridge->encoder->bridge_chain)) {
>> +       /* If dw-hdmi is the first or only bridge, avoid negociating with ourselves */
>> +       if (list_is_singular(&bridge->encoder->bridge_chain) ||
>> +           list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain)) {
>>                 *num_output_fmts = 1;
>>                 output_fmts[0] = MEDIA_BUS_FMT_FIXED;
>>  
>> @@ -2673,6 +2674,10 @@ static u32 *dw_hdmi_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
>>         if (!input_fmts)
>>                 return NULL;
>>  
>> +       /* If dw-hdmi is the first bridge fall-back to safe output format */
>> +       if (list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain))
>> +               output_fmt = MEDIA_BUS_FMT_FIXED;
>> +
>>         switch (output_fmt) {
>>         /* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */
>>         case MEDIA_BUS_FMT_FIXED:
> 
> Cheers
> 
> Marcel
> 

Thanks for the spelling fixes,

Neil