Re: [PATCH net-next v3 05/10] drivers: base: Add device_find_class()

[Florian Fainelli]

On 01/15/2017 03:04 AM, Greg KH wrote:
> On Sat, Jan 14, 2017 at 01:47:08PM -0800, Florian Fainelli wrote:
>> Add a helper function to lookup a device reference given a class name.
>> This is a preliminary patch to remove adhoc code from net/dsa/dsa.c and
>> make it more generic.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
>> ---
>>  drivers/base/core.c    | 19 +++++++++++++++++++
>>  include/linux/device.h |  1 +
>>  2 files changed, 20 insertions(+)
>>
>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>> index 020ea7f05520..3dd6047c10d8 100644
>> --- a/drivers/base/core.c
>> +++ b/drivers/base/core.c
>> @@ -2065,6 +2065,25 @@ struct device *device_find_child(struct device *parent, void *data,
>>  }
>>  EXPORT_SYMBOL_GPL(device_find_child);
>>  
>> +static int dev_is_class(struct device *dev, void *class)
>> +{
>> +	if (dev->class != NULL && !strcmp(dev->class->name, class))
>> +		return 1;
>> +
>> +	return 0;
>> +}
>> +
>> +struct device *device_find_class(struct device *parent, char *class)
> 
> Why are you using the char * for a class, and not just a pointer to
> "struct class"?  That seems to be the most logical one, no need to rely
> on string comparisons here.

A more reflective name of what that does would probably be
device_find_by_class_name() or something alike.

> 
> Also, what is this being used for?  You aren't trying to walk up the
> device heirachy to find a specific "type" of device, are you?  If so,
> ugh, I ranted about this in the past when the hyperv driver was trying
> to do such a thing...

What's a better way to do that though?

> 
>> +{
>> +	if (dev_is_class(parent, class)) {
>> +		get_device(parent);
>> +		return parent;
>> +	}
>> +
>> +	return device_find_child(parent, class, dev_is_class);
> 
> You are trying to find a peer device with the same parent that belongs
> to a specific class?

Correct, network devices, and MDIO bus devices usually (always?) set
dev.parent.

> 
> Again, what is this being used for?

See my other replies in patches 6, 7 and how it is used in patches 8 and
10 for instance.

> 
> And all exported driver core functions should have full kerneldoc
> information for them so that people know how to use them, and what the
> constraints are (see device_find_child() as an example.)  Please do that
> here as well because you are returning a pointer to a structure with the
> reference count incremented, callers need to know that.

Sure.
-- 
Florian