Re: [PATCH v4 2/2] PCI: mediatek-gen3: Add support for restricting link width

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

Il 04/11/24 14:20, Krzysztof Wilczyński ha scritto:
> 
> Hello,
> 
>> +	ret = of_property_read_u32(dev->of_node, "num-lanes", &num_lanes);
>> +	if (ret == 0) {
>> +		if (num_lanes == 0 || num_lanes > 16 || (num_lanes != 1 && num_lanes % 2))
>> +			dev_warn(dev, "Invalid num-lanes, using controller defaults\n");
>> +		else
>> +			pcie->num_lanes = num_lanes;
>> +	}
>> +
>>   	return 0;
>>   }
> 
> If you were to handle non-zero return value as an error here, perhaps the
> property has not been set, then we could reduce the indentation here.
> 
> Something like this, perhaps?
> 
>    ret = of_property_read_u32(dev->of_node, "num-lanes", &num_lanes);
>    if (ret) {
>            dev_err(dev, "Failed to read num-lanes: %d\n", ret);
>            return ret;
>    }
>    
>    if (!num_lanes || num_lanes > 16 || (num_lanes != 1 && num_lanes % 2))
>    	dev_warn(dev, "Invalid num-lanes, using controller defaults\n");
>    else
>    	pcie->num_lanes = num_lanes;
> 
> Does this make sense here?  Thoughts?
> 
> 	Krzysztof


Sorry I've just seen this email.

There's a problem here: this property has to be optional - and if you change that
to return like that, you're breaking compatibility with older device trees, which
are not specifying any "num-lanes" property.

Please remember that of_property_read_u32() returns:
  - 0 on success
  - -EINVAL if the property does not exist
  - -ENODATA or -EOVERFLOW

Please either keep the error checking like I wrote, or alternatively you can do..

ret = of_property_read_u32(...)
if (ret != -EINVAL) {
	dev_err(dev, "Failed to read num-lanes: %d\n", ret);
	return ret;
} else {
	if (num_lanes == 0 || ..... etc etc)
		dev_warn()
	else
		pcie->num_lanes = num_lanes
}

Cheers,
Angelo