linux-kernel - Re: [PATCH 2/2] gpio: Add Realtek Otto GPIO support

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Date:   Mon, 15 Mar 2021 16:10:27 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Sander Vanheule <sander@...nheule.net>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bert Vermeulen <bert@...t.com>
Subject: Re: [PATCH 2/2] gpio: Add Realtek Otto GPIO support

On Mon, Mar 15, 2021 at 9:26 AM Sander Vanheule <sander@...nheule.net> wrote:

> Realtek MIPS SoCs (platform name Otto) have GPIO controllers with up to
> 64 GPIOs, divided over two banks. Each bank has a set of registers for
> 32 GPIOs, with support for edge-triggered interrupts.
>
> Each GPIO bank consists of four 8-bit GPIO ports (ABCD and EFGH). Most
> registers pack one bit per GPIO, except for the IMR register, which
> packs two bits per GPIO (AB-CD).
>
> Although the byte order is currently assumed to have port A..D at offset
> 0x0..0x3, this has been observed to be reversed on other, Lexra-based,
> SoCs (e.g. RTL8196E/97D/97F).
>
> Interrupt support is disabled for the fallback devicetree-compatible
> 'realtek,otto-gpio'. This allows for quick support of GPIO banks in
> which the byte order would be unknown. In this case, the port ordering
> in the IMR registers may not match the reversed order in the other
> registers (DCBA, and BA-DC or DC-BA).
>
> Signed-off-by: Sander Vanheule <sander@...nheule.net>

Overall this is a beautiful driver and it makes use of all the generic
frameworks I can think of. I don't see any reason not to merge
it so:
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

The following is some notes and nitpicks, nothing blocking any
merge, more like discussion.

> +enum realtek_gpio_flags {
> +       GPIO_INTERRUPTS = BIT(0),
> +};

I suppose this looks like this because more flags will be introduced
when you add more functionality to the driver. Otherwise it seems
like overkill so a bool would suffice.

I would add a comment /* TODO: this will be expanded */

> +static inline u32 realtek_gpio_imr_bits(unsigned int pin, u32 value)
> +{
> +       return ((value & 0x3) << 2*(pin % 16));
> +}

I would explain a bit about this, obviouslt it is two bit per
line, but it took me some time to parse, so a comment
about the bit layout would be nice.

> +       unsigned int offset = pin/16;

Here that number appears again.

The use of GPIO_GENERIC and GPIO irqchip is flawless
and first class.

Thanks!
Linus Walleij