linux-kernel - Re: [PATCH v2] drm/bridge: dw-hdmi: use safe format when first in bridge chain

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Date:   Fri, 4 Feb 2022 15:28:07 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Robert Foss <robert.foss@...aro.org>
Cc:     laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, kieran.bingham@...asonboard.com,
        biju.das.jz@...renesas.com,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
Subject: Re: [PATCH v2] drm/bridge: dw-hdmi: use safe format when first in
 bridge chain

Hi,

On 04/02/2022 15:05, Robert Foss wrote:
> On Wed, 19 Jan 2022 at 13:28, Neil Armstrong <narmstrong@...libre.com> wrote:
>>
>> When the dw-hdmi bridge is in first place of the bridge chain, this
>> means there is no way to select an input format of the dw-hdmi HW
>> component.
>>
>> Since introduction of display-connector, negotiation was broken since
>> the dw-hdmi negotiation 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 negotiation.
>>
>> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
> 
> I think this is the wrong hash. Is 7cd70656d128 the actual hash?

Wow indeed, thanks for checking...

> 
>> was introduced to make negotiation work again by making display-connector
>> act as a pass-through concerning input & output format negotiation.
>>
>> But in the case where the dw-hdmi is single in the bridge chain, for
>> example on Renesas SoCs, with the display-connector bridge the dw-hdmi
>> is no more single, breaking output format.
>>
>> Reported-by: Biju Das <biju.das.jz@...renesas.com>
>> Bisected-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
>> Tested-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
>> Fixes: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks").
> 
> This hash too.
> 
>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>> ---
>> Changes since v1:
>> - Remove bad fix in dw_hdmi_bridge_atomic_get_input_bus_fmts
>> - Fix typos in commit message
>>
>>   drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 +++--
>>   1 file changed, 3 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..97cdc61b57f6 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;
>>
>> --
>> 2.25.1
>>
> 
> There are two checkstyle issues apart from the above mentioned hash
> issues, and I think we can ignore those. With the above mentioned
> issue fixed, feel free to add my r-b.
> 
> Reviewed-by: Robert Foss <robert.foss@...aro.org>

Thanks, I'll fix & resend with your r-b.

Neil