linux-kernel - Re: [PATCH 03/13] media: i2c: Defer probe if not endpoint found

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Date:   Fri, 23 Jul 2021 10:15:41 +0100
From:   Daniel Scally <djrscally@...il.com>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Yang Li <yang.lee@...ux.alibaba.com>,
        "open list:MEDIA INPUT INFRASTRUCTURE (V4L/DVB)" 
        <linux-media@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Yong Zhi <yong.zhi@...el.com>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Tianshu Qiu <tian.shu.qiu@...el.com>,
        Colin Ian King <colin.king@...onical.com>,
        laurent.pinchart@...asonboard.com, kieran.bingham@...asonboard.com
Subject: Re: [PATCH 03/13] media: i2c: Defer probe if not endpoint found

Hi Paul

On 23/07/2021 08:49, Paul Kocialkowski wrote:
> Hi Daniel,
>
> On Thu 22 Jul 21, 21:33, Daniel Scally wrote:
>> The ov8865 driver is one of those that can be connected to a CIO2
>> device by the cio2-bridge code. This means that the absence of an
>> endpoint for this device is not necessarily fatal, as one might be
>> built by the cio2-bridge when it probes. Return -EPROBE_DEFER if no
>> endpoint is found rather than a fatal error.
> Is this an error that you have actually seen in practice?


Yes

> My understanding is that this function should return the handle to the *local*
> fwnode graph endpoint, which relates to the static device-tree description
> and should be unrelated to another driver probing.
>
> So as far as I can see, this should not be needed (but correct me if I'm wrong).


It's a newly possible scenario - some laptops with Intel IPU3s have ACPI
that is _creative_,. and rather than define the endpoints in an ACPI
device's _DSD they're encoded within a buffer that's against the sensor
devices instead. We're parsing those out and building the fwnode graph
using software nodes in the ipu3-cio2 driver:


https://elixir.bootlin.com/linux/v5.14-rc2/source/drivers/media/pci/intel/ipu3/cio2-bridge.c#L166


But that means there's no endpoint for the sensor until ipu3-cio2 has
probed.


Thanks

Dan

>
> Cheers,
>
> Paul
>
>> Signed-off-by: Daniel Scally <djrscally@...il.com>
>> ---
>>  drivers/media/i2c/ov8865.c | 6 ++----
>>  1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/media/i2c/ov8865.c b/drivers/media/i2c/ov8865.c
>> index 2ef146e7e7ef..66182142c28b 100644
>> --- a/drivers/media/i2c/ov8865.c
>> +++ b/drivers/media/i2c/ov8865.c
>> @@ -2796,10 +2796,8 @@ static int ov8865_probe(struct i2c_client *client)
>>  	/* Graph Endpoint */
>>  
>>  	handle = fwnode_graph_get_next_endpoint(dev_fwnode(dev), NULL);
>> -	if (!handle) {
>> -		dev_err(dev, "unable to find endpoint node\n");
>> -		return -EINVAL;
>> -	}
>> +	if (!handle)
>> +		return -EPROBE_DEFER;
>>  
>>  	sensor->endpoint.bus_type = V4L2_MBUS_CSI2_DPHY;
>>  
>> -- 
>> 2.25.1
>>