linux-kernel - Re: [PATCH v3 1/2] drm/bridge: sii902x: Fix mode

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Date: Fri, 24 May 2024 17:54:02 +0530
From: Jayesh Choudhary <j-choudhary@...com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: <linux-kernel@...r.kernel.org>, <andrzej.hajda@...el.com>,
        <neil.armstrong@...aro.org>, <rfoss@...nel.org>,
        <Laurent.pinchart@...asonboard.com>, <sam@...nborg.org>,
        <mripard@...nel.org>, <dri-devel@...ts.freedesktop.org>,
        <jonas@...boo.se>, <jernej.skrabec@...il.com>,
        <maarten.lankhorst@...ux.intel.com>, <tzimmermann@...e.de>,
        <airlied@...il.com>, <daniel@...ll.ch>, <a-bhatia1@...com>
Subject: Re: [PATCH v3 1/2] drm/bridge: sii902x: Fix mode_valid hook

Hello Dmitry,

On 24/05/24 15:11, Dmitry Baryshkov wrote:
> On Fri, May 24, 2024 at 03:05:08PM +0530, Jayesh Choudhary wrote:
>> Currently, mode_valid hook returns all mode as valid and it is
>> defined only in drm_connector_helper_funcs. With the introduction of
>> 'DRM_BRIDGE_ATTACH_NO_CONNECTOR', connector is not initialized in
>> bridge_attach call for cases when the encoder has this flag enabled.
>> So add the mode_valid hook in drm_bridge_funcs as well with proper
>> clock checks for maximum and minimum pixel clock supported by the
>> bridge.
>>
>> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>

[...]

>> +
>>   static enum drm_mode_status sii902x_mode_valid(struct drm_connector *connector,
>>   					       struct drm_display_mode *mode)
>>   {
>> -	/* TODO: check mode */
>> +	struct sii902x *sii902x = connector_to_sii902x(connector);
>> +	const struct drm_display_mode *mod = mode;
>>   
>> -	return MODE_OK;
>> +	return sii902x_validate(sii902x, mod);
> 
> There is no need to. The drm_bridge_chain_mode_valid() should take care
> of calling bridge's mode_valid callback and rejecting the mode if it is
> not accepted.

I need some clarity here.

IIRC, if the bridge does initialize the connector in case
where the encoder does not attach the bridge with the
DRM_BRIDGE_ATTACH_NO_CONNECTOR (DBANC) flag (referring to tidss
encoder before we implemented the DBANC feature), then
drm_connector_helper_func are called and drm_bridge_funcs
are NOT called (atleast from what I have seen in detect
hook for cdns-mhdp-8546 driver which is there in both
structures).

I do not have any platform to test non-DBANC encoders.
And I did not want to break any platform that were still using
bridge_attach without DBANC flag.
That is why I kept mode_valid hook in both structures.

Are you implying that if connector_helper_funcs are not there
then there will be some sort of fallback to bridge_funcs instead
of passthrough for mode_valid check? Because that goes against my
previous observations.

Thanks,
Jayesh