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

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Message-ID: <5bf589c6-6ba9-434a-b7da-eb0c09284dcd@ti.com>
Date: Mon, 27 May 2024 12:53:53 +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



On 25/05/24 01:16, Dmitry Baryshkov wrote:
> On Fri, May 24, 2024 at 05:54:02PM +0530, Jayesh Choudhary wrote:
>> 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).
> 
> There are different kinds of bridge_funcs. detect is a part of the
> connector-related interface, so it is not called by the drm core. On the
> other hand functions like mode_valid, enable/disable, etc. are called
> for all bridges.
> 

Oh okay!
Thanks for clarifying.

>> 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.
> 
> Not quite. See how drm_atomic_heler uses bridge_funcs.
> 

I will do that and spin another revision with the suggested changes.

Warm Regards,
Jayesh