linux-kernel - Re: [PATCH] drm/bridge: sii902x: add support for DRM_BRIDGE_ATTACH_NO

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Date:   Mon, 8 Aug 2022 11:51:44 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Dmitry Osipenko <digetx@...il.com>, andrzej.hajda@...el.com,
        robert.foss@...aro.org, Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>
Cc:     jernej.skrabec@...il.com, jonas@...boo.se,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Laurent.pinchart@...asonboard.com
Subject: Re: [PATCH] drm/bridge: sii902x: add support for
 DRM_BRIDGE_ATTACH_NO_CONNECTOR

On 08/08/2022 11:15, Neil Armstrong wrote:
> Hi Dmitry,
> 
> On 31/07/2022 22:07, Dmitry Osipenko wrote:
>> 13.01.2022 17:43, Neil Armstrong пишет:
>>> This adds support for DRM_BRIDGE_ATTACH_NO_CONNECTOR by adding the
>>> bridge get_edid() and detect() callbacks after refactoring the connector
>>> get_modes() and connector_detect() callbacks.
>>>
>>> In order to keep the bridge working, extra code in get_modes() has been
>>> moved to more logical places.
>>>
>>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>>> ---
>>>   drivers/gpu/drm/bridge/sii902x.c | 129 ++++++++++++++++++++++++-------
> 
> 1 file changed, 99 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/bridge/sii902x.c b/drivers/gpu/drm/bridge/sii902x.c
>>> index 89558e581530..65549fbfdc87 100644
>>> --- a/drivers/gpu/drm/bridge/sii902x.c
>>> +++ b/drivers/gpu/drm/bridge/sii902x.c

[...]

>>>       }
>>> +    endpoint = of_graph_get_endpoint_by_regs(dev->of_node, 1, -1);
>>> +    if (endpoint) {
>>> +        struct device_node *remote = of_graph_get_remote_port_parent(endpoint);
>>> +
>>> +        of_node_put(endpoint);
>>> +        if (!remote) {
>>> +            dev_err(dev, "Endpoint in port@1 unconnected\n");
>>> +            return -ENODEV;
>>> +        }
>>> +
>>> +        if (!of_device_is_available(remote)) {
>>> +            dev_err(dev, "port@1 remote device is disabled\n");
>>> +            of_node_put(remote);
>>> +            return -ENODEV;
>>> +        }
>>> +
>>> +        sii902x->next_bridge = of_drm_find_bridge(remote);
>>> +        of_node_put(remote);
>>> +        if (!sii902x->next_bridge)
>>> +            return -EPROBE_DEFER;
>>
>> Hi,
>>
>> This patch broke ARM/QEMU vexpress display because of_drm_find_bridge()
>> always fail with -EPROBE_DEFER. Reverting this patch returns display
>> back. Please fix or revert, thanks in advance.
> 
> Can you share a QEMU cmdline to reproduce ?

Actually the vexpress DT has multiple input ports instead of a single input port at @0
and an output port at @1 like documented in the bindings:

vexpress-v2m.dtsi#L303-L307:
ports {
	#address-cells = <1>;
	#size-cells = <0>;

	/*
	 * Both the core tile and the motherboard routes their output
	 * pads to this transmitter. The motherboard system controller
	 * can select one of them as input using a mux register in
	 * "arm,vexpress-muxfpga". The Vexpress with the CA9 core tile is
	 * the only platform with this specific set-up.
	 */
	port@0 {
		reg = <0>;
		dvi_bridge_in_ct: endpoint {
			remote-endpoint = <&clcd_pads_ct>;
		};
	};
	port@1 {
		reg = <1>;
		dvi_bridge_in_mb: endpoint {
			remote-endpoint = <&clcd_pads_mb>;
		};
	};
};

bindings:
   ports:
     $ref: /schemas/graph.yaml#/properties/ports

     properties:
       port@0:
         $ref: /schemas/graph.yaml#/properties/port
         description: Parallel RGB input port

       port@1:
         $ref: /schemas/graph.yaml#/properties/port
         description: HDMI output port

       port@3:
         $ref: /schemas/graph.yaml#/properties/port
         description: Sound input port

The patch is conform to the bindings, the DT was working but is actually not valid.

Neil

> 
> Neil