linux-kernel - Re: [PATCH v2 1/7] drm/bridge: ps8640: Get the EDID from eDP control

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Date:   Fri, 17 Apr 2020 16:51:08 +0200
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     linux-kernel@...r.kernel.org,
        Collabora Kernel ML <kernel@...labora.com>,
        matthias.bgg@...il.com, drinkcat@...omium.org, hsinyi@...omium.org,
        Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Jonas Karlman <jonas@...boo.se>,
        Neil Armstrong <narmstrong@...libre.com>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 1/7] drm/bridge: ps8640: Get the EDID from eDP control

Hi Laurent,

On 16/4/20 19:22, Laurent Pinchart wrote:
> Hi Enric,
> 
> Thank you for the patch.
> 
> On Thu, Apr 16, 2020 at 05:57:13PM +0200, Enric Balletbo i Serra wrote:
>> The PS8640 DSI-to-eDP bridge can retrieve the EDID, so implement the
>> .get_edid callback and set the flag to indicate the core to use it.
>>
>> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
>> ---
>>
>> Changes in v2: None
>>
>>  drivers/gpu/drm/bridge/parade-ps8640.c | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
>> index d3a53442d449..956b76e0a44d 100644
>> --- a/drivers/gpu/drm/bridge/parade-ps8640.c
>> +++ b/drivers/gpu/drm/bridge/parade-ps8640.c
>> @@ -242,8 +242,18 @@ static int ps8640_bridge_attach(struct drm_bridge *bridge,
>>  	return ret;
>>  }
>>  
>> +static struct edid *ps8640_bridge_get_edid(struct drm_bridge *bridge,
>> +					   struct drm_connector *connector)
>> +{
>> +	struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
>> +
>> +	return drm_get_edid(connector,
>> +			    ps_bridge->page[PAGE0_DP_CNTL]->adapter);
> 
> This will only work if the DDC signals are connected to the PS8640
> (quite obviously). Is that guaranteed, or could some systems connect
> them directory to an SoC I2C controller ?

It is possible but IMHO opinion this is hardware tricky, I mean, ps8640 outputs
eDP interface and the panel is an eDP interface, so I'd expect hardware
engineers do a pin to pin design, not routing the DDC signals to the SoC
directly ignoring the eDP interface.

> In the latter case we would
> have to report this in the DT bindings of the PS8640. That's not
> blocking for this patch, I am just wondering, as I would have expected
> the driver to already expose EDID one way or another if this was
> available and used.
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> 
>> +}
>> +
>>  static const struct drm_bridge_funcs ps8640_bridge_funcs = {
>>  	.attach = ps8640_bridge_attach,
>> +	.get_edid = ps8640_bridge_get_edid,
>>  	.post_disable = ps8640_post_disable,
>>  	.pre_enable = ps8640_pre_enable,
>>  };
>> @@ -296,6 +306,8 @@ static int ps8640_probe(struct i2c_client *client)
>>  
>>  	ps_bridge->bridge.funcs = &ps8640_bridge_funcs;
>>  	ps_bridge->bridge.of_node = dev->of_node;
>> +	ps_bridge->bridge.ops = DRM_BRIDGE_OP_EDID;
>> +	ps_bridge->bridge.type = DRM_MODE_CONNECTOR_eDP;
>>  
>>  	ps_bridge->page[PAGE0_DP_CNTL] = client;
>>  
>