Re: [PATCH v2 11/12] media: mt9m114: Return -EPROBE_DEFER if no endpoint is found

[Hans de Goede <hansg@kernel.org>]

Hi Laurent,

Thank you for your reviews. I agree with most of your
comments and I'll address them when I can make some time.

On 3-Jun-25 1:03 PM, Laurent Pinchart wrote:
> Hi Hans,
> 
> Thank you for the patch.
> 
> On Sat, May 31, 2025 at 06:31:46PM +0200, Hans de Goede wrote:
>> With IPU# bridges, endpoints may only be created when the IPU bridge is
>> initialized. This may happen after the sensor driver's first probe().
>>
>> Signed-off-by: Hans de Goede <hansg@kernel.org>
>> ---
>>  drivers/media/i2c/mt9m114.c | 11 +++++++----
>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/media/i2c/mt9m114.c b/drivers/media/i2c/mt9m114.c
>> index c4d3122d698e..72914c47ec9a 100644
>> --- a/drivers/media/i2c/mt9m114.c
>> +++ b/drivers/media/i2c/mt9m114.c
>> @@ -2399,11 +2399,14 @@ static int mt9m114_parse_dt(struct mt9m114 *sensor)
>>  	struct fwnode_handle *ep;
>>  	int ret;
>>  
>> +	/*
>> +	 * Sometimes the fwnode graph is initialized by the bridge driver,
>> +	 * wait for this.
>> +	 */
>>  	ep = fwnode_graph_get_next_endpoint(fwnode, NULL);
>> -	if (!ep) {
>> -		dev_err(&sensor->client->dev, "No endpoint found\n");
>> -		return -EINVAL;
>> -	}
>> +	if (!ep)
>> +		return dev_err_probe(&sensor->client->dev, -EPROBE_DEFER,
>> +				     "waiting for fwnode graph endpoint\n");
> 
> That's a bit annoying, as in non-ACPI systems we'll then get probe
> deferral, making the issue more difficult to debug.

With "then" I assume you mean when the fwnode graph endpoint is missing
on DT systems ?

> Is there a way, on IPU-based systems, to delay probing the sensor until
> the bridge has been initialized ?

Waiting for the fwnode graph endpoint to show up is the way to wait for
bridge init we (Sakari and me) have agreed upon, this is done on all
drivers used on x86/ACPI platforms.

Note that by using dev_err_probe() here and not just
"return -EPROBE_DEFER" the kernel will log a message
during boot some time (1 minute?) after the last probe
has succeeded about devices with a deferred probe pending
logging the reason passed to dev_err_probe(), so debugging
this is should not be that much of an issue. There will still
be a log message, it is just that it will be logged a bit later
rather then directly at probe time.

Regards,

Hans







 I suppose this is a question for
> Sakari too.
> 
>>  
>>  	sensor->bus_cfg.bus_type = V4L2_MBUS_UNKNOWN;
>>  	ret = v4l2_fwnode_endpoint_alloc_parse(ep, &sensor->bus_cfg);
>