Re: [PATCH v2 2/2] hwmon: ltc4282: add support for the LTC4282 chip

From: Guenter Roeck <linux@roeck-us.net>
To: "Andy Shevchenko" <andy@kernel.org>, "Nuno Sá" <noname.nuno@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>,
	nuno.sa@analog.com, linux-hwmon@vger.kernel.org,
	devicetree@vger.kernel.org, linux-doc@vger.kernel.org,
	Jean Delvare <jdelvare@suse.com>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Bartosz Golaszewski <brgl@bgdev.pl>
Subject: Re: [PATCH v2 2/2] hwmon: ltc4282: add support for the LTC4282 chip
Date: Thu, 30 Nov 2023 06:39:25 -0800	[thread overview]
Message-ID: <42f71f77-7b58-4487-8cc2-52d870759890@roeck-us.net> (raw)
In-Reply-To: <ZWiP3i80KnVk9qyx@smile.fi.intel.com>

On 11/30/23 05:36, Andy Shevchenko wrote:
> On Thu, Nov 30, 2023 at 11:20:32AM +0100, Nuno Sá wrote:
>> On Wed, 2023-11-29 at 21:55 +0100, Linus Walleij wrote:
>>> On Wed, Nov 29, 2023 at 5:08 PM Nuno Sá <noname.nuno@gmail.com> wrote:
>>>
>>>> Cool, I actually thought that having the direction + get/set stuff would be weird
>>>> given the fact that we can only PULL_LOW or HIGH_Z the pins.
>>>
>>> There are several drivers in the kernel that implement .set_config(),
>>> it's existing and should be enabled if it has uses.
>>
>> Yeah, it might make sense to support it specially for the input case. AFAICT, if I
>> use the .set_config() (but from a quick look I think we will need to add support for
>> it in gpiolib for the high-z configuration), then I can't use the gpio_regmap stuff.
>> As the driver stands I don't think I could do it anyways because setting gpio2-3 and
>> alert requires to write 0 on the register rather than 1. But again, I'm still very
>> suspicious about the whole thing. The datasheet states:
>>
>> "GPIO1-GPIO3 and ALERT all have comparators monitoring
>> the voltage on these pins with a threshold of 1.28V even when
>> the pins are configured as outputs."
>>
>> But we can't really set the direction for gpio2-3 and the alert pins (only getting
>> the level and setting it as PULL_LOW or HIGH_Z. gpio1 is the only one where we can
>> configure it as input or open drain ouput. Bah, I'll try to see if someone internally
>> can shed some light on this.
> 
> I have better proposal. If these GPIOs are not needed for the main
> functionality of the hardware, can we just left it out for now and implement
> later if required?
> 

I very much agree.

Guenter