linux-kernel - RE: [PATCH v1 2/2] gpio: ds4520: Add ADI DS4520 Regulator Support

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Message-ID: <MN2PR03MB5168D7940E322DFC0A1A3148E7679@MN2PR03MB5168.namprd03.prod.outlook.com>
Date:   Mon, 24 Apr 2023 15:39:05 +0000
From:   "Sahin, Okan" <Okan.Sahin@...log.com>
To:     Michael Walle <michael@...le.cc>
CC:     "andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1 2/2] gpio: ds4520: Add ADI DS4520 Regulator Support

>Am 2023-04-09 16:25, schrieb Sahin, Okan:
>>> Fri, Apr 07, 2023 at 03:48:25PM +0200, Linus Walleij kirjoitti:
>>>> On Wed, Apr 5, 2023 at 3:57 PM Michael Walle <michael@...le.cc>
>>>> wrote:
>>>>
>>>> > OTOH I'm not sure the driver is doing it correctly, because it also
>>>> > seems to switch the pullup resisters together with the direction.
>>>> > I'm not sure that is correct. So there might be just one register
>>>> > involved after all and the GPIO_REGMAP should work again.
>>>>
>>>> I'm pretty sure that should be in the .set_config() callback.
>>>>
>>>> > Also, according to the datasheet this has some nv memory (to set the
>>>> > initial state of the GPIOs [?]). So it should really be a
>>>> > multi-function device. I'm not sure if this has to be considered
>>>> > right from the beginning or if the device support can start with
>>>> > GPIO only and later be transitioned to a full featured MFD (probably with
>nvmem
>>> support).
>>>>
>>>> That's a bit of a soft definition.
>>>>
>>>> If the chip is *only* doing GPIO and nvram it can be a GPIO-only
>>>> device I think.
>>>>
>>>> The precedent is a ton of ethernet drivers with nvram for storing
>>>> e.g.
>>>> the MAC address. We don't make all of those into MFDs, as the nvram
>>>> is
>>>> closely tied to the one and only function of the block.
>>>
>>> I agree with Linus. This should be part of the actual (main) driver
>>> for the chip as many
>>> do (like USB to serial adapters that have GPIO capability).
>
>You mean the gpio driver is calling nvmem_register()? Yeah I agree, that
>should work.
>
>> I think gpio_regmap is not suitable for this driver as Michael stated.
>> https://www.analog.com/media/en/technical-documentation/data-
>sheets/ds4520.pdf
>> Please check block diagram. There are two input registers that control
>> gpio state
>> so gpio_regmap does not look ok for this. Am I missing something?
>
>You mean F8/F9? That will work as they are for different GPIOs. What
>doesn't work with gpio-regmap is when you need to modify two different
>registers for one GPIO. Have a look at gpio_regmap_get() and
>gpio_regmap_set(). If the default gpio_regmap_simple_xlate() doesn't
>work
>you can use your own .xlate() op.
>

Actually, I checked the functions that you suggested, but as far as I understand
they might work if there would be one bit to set direction or value. However,
this is not the case for ds4520. In other words, if I want to set the gpio direction
as output, I need to set a corresponding bit for both F0 and F1 registers.
In the document, you can see block diagram. I do not know why, but design is
not standard that’s why I think I can not use gpio-regmap.

>> Also, at this point I am not planning to add nvmem support.
>
>That is a pity, because that is the whole use case for this gpio
>expander,
>no? "Programmable Replacement for Mechanical Jumpers and Switches"

I can set "SEE" bit as "0" in the Configuration Register to write EEPROM so it might solve
issue.

>
>-michael

Regards,
Okan Sahin