linux-kernel - Re: [PATCH v4 5/5] gpio: syscon: Add support for the Xylon LogiCVC GPIOs

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Message-ID: <CACRpkdaSLsq-oA7t8OL6_6L+ivZE+a83M4JbTZ2HW5E1E7c6yw@mail.gmail.com>
Date:   Fri, 29 Nov 2019 10:24:58 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Lee Jones <lee.jones@...aro.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v4 5/5] gpio: syscon: Add support for the Xylon LogiCVC GPIOs

Hi Paul,

thanks for your patch!

On Thu, Nov 28, 2019 at 4:54 PM Paul Kocialkowski
<paul.kocialkowski@...tlin.com> wrote:

> The LogiCVC display hardware block comes with GPIO capabilities
> that must be exposed separately from the main driver (as GPIOs) for
> use with regulators and panels. A syscon is used to share the same
> regmap across the two drivers.
>
> Since the GPIO capabilities are pretty simple, add them to the syscon
> GPIO driver.
>
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
(...)
> +#define LOGICVC_CTRL_REG               0x40
> +#define LOGICVC_CTRL_GPIO_SHIFT                11
> +#define LOGICVC_CTRL_GPIO_BITS         5
> +
> +#define LOGICVC_POWER_CTRL_REG         0x78
> +#define LOGICVC_POWER_CTRL_GPIO_SHIFT  0
> +#define LOGICVC_POWER_CTRL_GPIO_BITS   4
> +
> +static void logicvc_gpio_offset(struct syscon_gpio_priv *priv,
> +                               unsigned offset, unsigned int *reg,
> +                               unsigned int *bit)
> +{
> +       if (offset >= LOGICVC_CTRL_GPIO_BITS) {
> +               *reg = LOGICVC_POWER_CTRL_REG;
> +
> +               /* To the (virtual) power ctrl offset. */
> +               offset -= LOGICVC_CTRL_GPIO_BITS;
> +               /* To the actual bit offset in reg. */
> +               offset += LOGICVC_POWER_CTRL_GPIO_SHIFT;
> +       } else {
> +               *reg = LOGICVC_CTRL_REG;
> +
> +               /* To the actual bit offset in reg. */
> +               offset += LOGICVC_CTRL_GPIO_SHIFT;
> +       }
> +
> +       *bit = BIT(offset);
> +}

The gpio-syscon.c is for simple syscons where the lines
you want to affect are nicely ordered in the registers.
It is intended to be generic.

This is kind of shoehorning a special case into the generic
code.

Isn't it more appropriate to create a specific driver for this
hardware?

Special get/set quirks for any possible quirky offset is
certainly not the way to go, if this should be supported
we need generic properties in struct syscon_gpio_data
to indicate the valid bits and offsets.

Yours,
Linus Walleij