linux-kernel - Re: [PATCH v4 02/11] drm/bridge: dw-hdmi: add max bpc connector property

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Message-ID: <09d315b8-22f3-a25a-1aea-9c5d50c634d6@baylibre.com>
Date:   Fri, 21 Feb 2020 09:50:18 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Jernej Škrabec <jernej.skrabec@...l.net>,
        a.hajda@...sung.com, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, boris.brezillon@...labora.com
Cc:     linux-amlogic@...ts.infradead.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 02/11] drm/bridge: dw-hdmi: add max bpc connector
 property

Hi Jernej,

On 17/02/2020 07:38, Jernej Škrabec wrote:
> Hi!
> 
> Dne četrtek, 06. februar 2020 ob 20:18:25 CET je Neil Armstrong napisal(a):
>> From: Jonas Karlman <jonas@...boo.se>
>>
>> Add the max_bpc property to the dw-hdmi connector to prepare support
>> for 10, 12 & 16bit output support.
>>
>> Signed-off-by: Jonas Karlman <jonas@...boo.se>
>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>> ---
>>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c index
>> 9e0927d22db6..051001f77dd4 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>> @@ -2406,6 +2406,10 @@ static int dw_hdmi_bridge_attach(struct drm_bridge
>> *bridge) DRM_MODE_CONNECTOR_HDMIA,
>>  				    hdmi->ddc);
>>
>> +	drm_atomic_helper_connector_reset(connector);
> 
> Why is this reset needed?

I assume it's to allocate a new connector state to attach a the bpc propery.

But indeed, this helper is never used here, but only as callback to the drm_connector_funcs->reset.

But, amdgpu calls :
	/*
	 * Some of the properties below require access to state, like bpc.
	 * Allocate some default initial connector state with our reset helper.
	 */
	if (aconnector->base.funcs->reset)
		aconnector->base.funcs->reset(&aconnector->base);

which is the same.

Neil

> 
> Best regards,
> Jernej
> 
>> +
>> +	drm_connector_attach_max_bpc_property(connector, 8, 16);
>> +
>>  	if (hdmi->version >= 0x200a && hdmi->plat_data->use_drm_infoframe)
>>  		drm_object_attach_property(&connector->base,
>>  			connector->dev-
>> mode_config.hdr_output_metadata_property, 0);
> 
> 
> 
>