Re: [PATCH] hwmon: (jc42) Fix name to have no illegal characters

[Guenter Roeck <linux@roeck-us.net>]

On 4/17/20 6:47 AM, Jean Delvare wrote:
> On Fri, 17 Apr 2020 12:32:55 +0200, Sascha Hauer wrote:
>> On Fri, Apr 17, 2020 at 11:55:03AM +0200, Jean Delvare wrote:
>>> On Fri, 17 Apr 2020 11:28:53 +0200, Sascha Hauer wrote:  
>>>> The jc42 driver passes I2C client's name as hwmon device name. In case
>>>> of device tree probed devices this ends up being part of the compatible
>>>> string, "jc-42.4-temp". This name contains hyphens and the hwmon core
>>>> doesn't like this:
>>>>
>>>> jc42 2-0018: hwmon: 'jc-42.4-temp' is not a valid name attribute, please fix
>>>>
>>>> This changes the name to "jc42" which doesn't have any illegal
>>>> characters.  
>>>
>>> I don't think "jc-42.4-temp" is a valid i2c client name either.  
>>
>> What makes the name invalid then? I am not aware of any constraints of
>> i2c client names.
> 
> Historically hwmon devices were i2c devices so libsensors would use
> the i2c client name as the device name, and still does as a fallback if
> memory serves. Therefore whatever rule applies to hwmon names would
> also apply to i2c names (in the context of hwmon devices) even though
> this is not enforced.
> 
>>> I believe this should be fixed at the of->i2c level, rather than the
>>> i2c->hwmon level.  
>>
>> Are you suggesting a character conversion from hyphens to underscores or
>> similar in the i2c core?
> 
> No, my point is that from a userspace perspective it shouldn't matter
> if the device comes from the OF tree or not. So the device name should
> be the same, i.e. the i2c client should be named "jc42" always. That's
> what happens for all other devices I checked, simply because it turns
> out that their OF compatible string is in the form
> <vendor_name>,<linux_i2c_client_name>, so when you strip the vendor
> name you get the right name directly.
> 
> My knowledge of the OF subsystem is fairly limited though, so I have no
> idea if it is possible to enforce a specific name like that at an early
> stage. The proper name can't be guessed by i2c-core, so ideally the
> conversion should be provided by the driver itself. I see that struct
> of_device_id has a "name" field, can it be used for that purpose? If
> not, I suppose the "data" field could be used for that.
> 
>>> Not sure how other drivers are dealing with that, it
>>> seems that in most cases the name part of the compatible string matches
>>> exactly the expected client name so no conversion is needed.  
>>
>> Other i2c hwmon drivers I found do not have any hyphens in their
>> compatible string, so they are at least not hit by this message.
> 
> I drew the same conclusion here, and your patch is definitely better
> than nothing as it fixes a real problem, however it is not prefect due
> to the reason explained above, plus the fact that it would break if the
> driver ever supports more than one device type (say JEDEC releases JC43
> tomorrow and we add support... you code forces the name to "jc42" even
> if the OF name was something other than "jc-42.4-temp").
> 

The driver should really list all supported devices (not the standard).
It could/should have a generic property name to match, but I have no idea
what that should be. There are existing compatible properties named
"jedec,ufs-1.1" and similar, so maybe the current compatible string
isn't as bad as I thought.

Still, we need to do something. I am open to suggestions.

Guenter