linux-kernel - Re: [PATCH v5 12/13] gpio: Add support for Airoha EN7523 GPIO controller

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Date:   Thu, 2 Dec 2021 20:02:48 +0100
From:   John Crispin <john@...ozen.org>
To:     Felix Fietkau <nbd@....name>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Bartosz Golaszewski <brgl@...ev.pl>,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v5 12/13] gpio: Add support for Airoha EN7523 GPIO
 controller



On 02.12.21 18:59, Felix Fietkau wrote:
> 
> On 2021-12-02 02:47, Linus Walleij wrote:
>> Hi Felix!
>>
>> Thanks for your patch!
>>
>> On Mon, Nov 29, 2021 at 4:54 PM Felix Fietkau <nbd@....name> wrote:
>>
>>> From: John Crispin <john@...ozen.org>
>>>
>>> Airoha's GPIO controller on their ARM EN7523 SoCs consists of two 
>>> banks of 32
>>> GPIOs. Each instance in DT is for an single bank.
>>>
>>> Signed-off-by: John Crispin <john@...ozen.org>
>>> Signed-off-by: Felix Fietkau <nbd@....name>
>>
>> (...)
>>> +config GPIO_EN7523
>>> +       tristate "Airoha GPIO support"
>>> +       depends on ARCH_AIROHA
>>> +       default ARCH_AIROHA
>>> +       select GPIO_GENERIC
>>
>> Yes that looks applicable, but why isn't it used?
>>
>> The few 32-bit registers look like an ideal candidate for
>> using the generic GPIO. Check similar drivers such as
>> drivers/gpio/gpio-ftgpio010.c and how it uses
>> bgpio_init() and the nice doc for bgpio_init() in
>> drivers/gpio/gpio-mmio.c.
> I just looked at the datasheet and the driver code again, and I think 
> EN7523 is too strange for proper generic GPIO support.
> 
> For each bank there are two control registers (not consecutive), which 
> have 2-bit fields for every GPIO line to control direction. No idea why 
> 2 bits per line, because only values 0 and 1 are valid, the rest are 
> reserved.
> For lines configured as output, an extra output-enable bit also needs to 
> be set in a separate register before output values can be written.
> 
> The code does use bgpio to read/write values, but that's about it.
> I don't think it would do the generic GPIO code any good to support this 
> weirdness.
> 
> - Felix
Hi Linus,
I sent an email to you 16.06.21 explaining all of this and you replied, 
telling me that this approach is the most reasonable one to take.
	John