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

From: Daniel Scally <djrscally@gmail.com>
To: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Ezequiel Garcia <ezequiel@collabora.com>,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	Yang Li <yang.lee@linux.alibaba.com>,
	"open list:MEDIA INPUT INFRASTRUCTURE (V4L/DVB)" 
	<linux-media@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	Yong Zhi <yong.zhi@intel.com>, Bingbu Cao <bingbu.cao@intel.com>,
	Tianshu Qiu <tian.shu.qiu@intel.com>,
	Colin Ian King <colin.king@canonical.com>,
	laurent.pinchart@ideasonboard.com,
	kieran.bingham@ideasonboard.com
Subject: Re: [PATCH 03/13] media: i2c: Defer probe if not endpoint found
Date: Fri, 23 Jul 2021 10:15:41 +0100	[thread overview]
Message-ID: <32df477e-754d-4432-dddc-668596990dcf@gmail.com> (raw)
In-Reply-To: <YPp0eCIawk2TGQ6Z@aptenodytes>

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@gmail.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
>>