From: "Nuno Sá" <noname.nuno@gmail.com>
To: Andy Shevchenko <andy@kernel.org>
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>,
Guenter Roeck <linux@roeck-us.net>,
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 16:20:13 +0100 [thread overview]
Message-ID: <a4bd59df0c5bc1be5d0d6f11b968fd61a59ee2e0.camel@gmail.com> (raw)
In-Reply-To: <ZWiP3i80KnVk9qyx@smile.fi.intel.com>
On Thu, 2023-11-30 at 15:36 +0200, 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?
>
Well, I did spent some time on the gpio thing so I would like to have it in but yeah,
no hard feelings if it does not go in.
So, I actually talk with some hw guys and the pull_low is not really like a pull_low
resistor. These pins are effectively an open drain. Which means, setting them as
input means setting them in high-z (turning off the mosffet) - and I do have a bug in
my code regarding this - Or if you want them as outputs you can set the level low
(and it will always be low - just turn on the mosffet) or you can also set high-z
which means it will be either low or high depending on your external circuitry. The
point is, you can still have your pin acting as a normal gpo if you accommodate your
circuitry for it (can also use these pins for things like buses).
Also got me thinking if a gpi vs gpo devicetree property would make sense. But I
would likely leave it more generic/relaxed for now (even though I think you would
need to be creative and actually use more HW to have the possibility of using these
pins as GPIs and GPOs at the same time).
- Nuno Sá
next prev parent reply other threads:[~2023-11-30 15:20 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-24 14:18 [PATCH v2 0/2] Add support for LTC4282 Nuno Sa via B4 Relay
2023-11-24 14:18 ` [PATCH v2 1/2] dt-bindings: hwmon: Add LTC4282 bindings Nuno Sa via B4 Relay
2023-11-25 11:56 ` Conor Dooley
2023-11-27 7:56 ` Nuno Sá
2023-11-27 17:33 ` Conor Dooley
2023-11-28 15:37 ` Rob Herring
2023-11-28 15:49 ` Nuno Sá
2023-11-24 14:18 ` [PATCH v2 2/2] hwmon: ltc4282: add support for the LTC4282 chip Nuno Sa via B4 Relay
2023-11-24 21:54 ` kernel test robot
2023-11-24 23:39 ` kernel test robot
2023-11-27 7:53 ` Nuno Sá
2023-11-27 8:10 ` Krzysztof Kozlowski
2023-11-27 8:12 ` Krzysztof Kozlowski
2023-11-27 8:44 ` Nuno Sá
2023-11-27 16:03 ` Andy Shevchenko
2023-11-28 16:50 ` Krzysztof Kozlowski
2023-11-28 17:01 ` Andy Shevchenko
2023-11-28 18:03 ` Guenter Roeck
2023-11-29 8:35 ` Nuno Sá
2023-11-29 8:45 ` Krzysztof Kozlowski
2023-11-29 8:56 ` Nuno Sá
2023-11-29 14:10 ` Linus Walleij
2023-11-29 14:13 ` Krzysztof Kozlowski
2023-11-29 14:29 ` Nuno Sá
2023-11-29 14:47 ` Guenter Roeck
2023-11-29 16:09 ` Nuno Sá
2023-11-27 10:20 ` kernel test robot
2023-11-29 14:49 ` Linus Walleij
2023-11-29 16:08 ` Nuno Sá
2023-11-29 16:18 ` Andy Shevchenko
2023-11-29 16:21 ` Nuno Sá
2023-11-29 17:07 ` Andy Shevchenko
2023-11-29 20:55 ` Linus Walleij
2023-11-30 10:20 ` Nuno Sá
2023-11-30 13:36 ` Andy Shevchenko
2023-11-30 14:39 ` Guenter Roeck
2023-11-30 15:20 ` Nuno Sá [this message]
2023-11-30 16:28 ` Guenter Roeck
2023-11-30 20:15 ` Linus Walleij
2023-12-01 12:34 ` Nuno Sá
2023-12-01 13:40 ` Linus Walleij
2023-12-01 15:24 ` Nuno Sá
2023-12-01 15:47 ` Andy Shevchenko
2023-12-01 16:04 ` Guenter Roeck
2023-12-01 16:24 ` Andy Shevchenko
2023-12-01 16:36 ` Guenter Roeck
2023-12-01 16:29 ` Nuno Sá
2023-12-01 16:46 ` Guenter Roeck
2023-12-02 9:42 ` Nuno Sá
2023-12-03 23:08 ` Linus Walleij
2023-12-04 8:20 ` Bartosz Golaszewski
2023-12-01 16:19 ` Nuno Sá
2023-12-01 16:23 ` Andy Shevchenko
2023-12-03 23:03 ` Linus Walleij
2023-12-04 8:53 ` Nuno Sá
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