linux-kernel - Re: [PATCH v2] dt-bindings: hwmon: tda38640: Add interrupt & regulator properties

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Message-ID: <980b8f03-ede4-479c-bbbb-f896fbac5c4b@roeck-us.net>
Date: Sat, 17 Feb 2024 13:52:13 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Conor Dooley <conor@...nel.org>
Cc: Naresh Solanki <naresh.solanki@...ements.com>,
 Jean Delvare <jdelvare@...e.com>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, mazziesaccount@...il.com,
 linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dt-bindings: hwmon: tda38640: Add interrupt &
 regulator properties

On 2/17/24 12:30, Conor Dooley wrote:
> On Sat, Feb 17, 2024 at 07:57:43AM -0800, Guenter Roeck wrote:
>> On 2/15/24 03:48, Conor Dooley wrote:
>>> On Wed, Feb 14, 2024 at 05:17:04PM -0800, Guenter Roeck wrote:
>>>> On 2/14/24 11:55, Conor Dooley wrote:
>>>> [ ... ]
>>>>>>> Why "vout0" if there's only one output? Is it called that in the
>>>>>>> documentation? I had a quick check but only saw it called "vout".
>>>>>>> Are there other related devices that would have multiple regulators
>>>>>>> that might end up sharing the binding?
>>>>>>>
>>>>>>
>>>>>> Primarily because that is what the PMBus core generates for the driver
>>>>>> because no one including me was aware that this is unacceptable
>>>>>> for single-output drivers.
>>>>>
>>>>> Is it unacceptable? If you're implying that I am saying it is, that's
>>>>> not what I was doing here - I'm just wondering why it was chosen.
>>>>> Numbering when there's only one seems odd, so I was just looking for the
>>>>> rationale.
>>>>>
>>>>
>>>> Given the tendency of corporate speak (aka "this was a good attempt" for
>>>> a complete screwup), and since this did come up before, I did interpret
>>>> it along that line. My apologies if that was not the idea.
>>>
>>> I'm not gonna go and decree that "vout0" is unacceptable, if it was
>>> called that in documentation that I had missed or was convention, I was
>>> just gonna say "okay, that sounds reasonable to me".
>>>
>>
>> "convention" only if lack of awareness how regulators are supposed to be named
>> is a convention.
> 
> They're "supposed" to be named whatever the binding says they are named,
> but as we've discovered none of these devices actually have bindings
> that allow regulators in the first place. I think they should be called
> whatever they're called in the documentation for the device, which in
> this case was "vout".
> 

I would agree. I'd even submit a yaml file extension for the affected drivers
to address that, but I realize that I am notoriously bad with doing that,
so I won't even try.

>>>> Still, I really don't know how to resolve this for existing PMBus drivers
>>>> which do register "vout0" even if there is only a single output regulator.
>>>
>>> I had a quick look at that series, none of the devices that I checked
>>> out there seem to have documented regulators at all. Some of the devices
>>> were only documented in trivial-devices.yaml. Relying on the naming of
>>> undocumented child nodes is a bug in those drivers & I guess nobody cares
>>> about dtbs_check complaints for those platforms. The example that was
>>> linked in the other thread doesn't even use a valid compatible :(
>>> 	https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/aspeed/aspeed-bmc-delta-ahe50dc.dts?id=8d3dea210042f54b952b481838c1e7dfc4ec751d#n21
>>> I guess it uses the i2c device ids to probe on that platform, or have
>>> I missed something there?
>>>
>>
>> I think that is correct. If I recall correctly, the I2C subsystem no longer
>> searches for compatible drivers by only looking at the device id in the
>> compatible node, so I guess one has to list "lm25066" instead of "ti,lm25066"
>> as compatible to get a match in the i2c subsystem. That is of course
>> completely wrong.
> 
> If the driver is probing based on i2c_device_id matching, is it correct to
> use DT to probe the regulators? (I don't know, that's not some sort of
> rhetorical question).

Looking into the lm25066 driver, it actually does support the "ti,lm25066"
compatible. Given that, I don't know why the dts file doesn't use it, especially
since the dts file was created after the compatible entry was added to the
lm25066 driver.

Guenter