linux-kernel - Re: [v3 PATCH 1/1] gpio: exar: access MPIO registers on cascaded chips

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Date:   Fri, 2 Sep 2022 09:18:49 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Qingtao Cao <qingtao.cao.au@...il.com>
Cc:     Qingtao Cao <qingtao.cao@...i.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [v3 PATCH 1/1] gpio: exar: access MPIO registers on cascaded chips

On Fri, Sep 2, 2022 at 9:15 AM Qingtao Cao <qingtao.cao.au@...il.com> wrote:
>
> When EXAR xr17v35x chips are cascaded in order to access the MPIO registers
> (part of the Device Configuration Registers) of the secondary chips, an offset
> needs to be applied based on the number of primary chip's UART channels.

Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
Thanks!

> Signed-off-by: Qingtao Cao <qingtao.cao@...i.com>
> ---
>  drivers/gpio/gpio-exar.c | 40 +++++++++++++++++++++++++++++++++++-----
>  1 file changed, 35 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpio/gpio-exar.c b/drivers/gpio/gpio-exar.c
> index d37de78247a6..482f678c893e 100644
> --- a/drivers/gpio/gpio-exar.c
> +++ b/drivers/gpio/gpio-exar.c
> @@ -21,6 +21,12 @@
>  #define EXAR_OFFSET_MPIOLVL_HI 0x96
>  #define EXAR_OFFSET_MPIOSEL_HI 0x99
>
> +/*
> + * The Device Configuration and UART Configuration Registers
> + * for each UART channel take 1KB of memory address space.
> + */
> +#define EXAR_UART_CHANNEL_SIZE 0x400
> +
>  #define DRIVER_NAME "gpio_exar"
>
>  static DEFINE_IDA(ida_index);
> @@ -31,26 +37,39 @@ struct exar_gpio_chip {
>         int index;
>         char name[20];
>         unsigned int first_pin;
> +       /*
> +        * The offset to the cascaded device's (if existing)
> +        * Device Configuration Registers.
> +        */
> +       unsigned int cascaded_offset;
>  };
>
>  static unsigned int
>  exar_offset_to_sel_addr(struct exar_gpio_chip *exar_gpio, unsigned int offset)
>  {
> -       return (offset + exar_gpio->first_pin) / 8 ? EXAR_OFFSET_MPIOSEL_HI
> -                                                  : EXAR_OFFSET_MPIOSEL_LO;
> +       unsigned int pin = exar_gpio->first_pin + (offset % 16);
> +       unsigned int cascaded = offset / 16;
> +       unsigned int addr = pin / 8 ? EXAR_OFFSET_MPIOSEL_HI : EXAR_OFFSET_MPIOSEL_LO;
> +
> +       return addr + (cascaded ? exar_gpio->cascaded_offset : 0);
>  }
>
>  static unsigned int
>  exar_offset_to_lvl_addr(struct exar_gpio_chip *exar_gpio, unsigned int offset)
>  {
> -       return (offset + exar_gpio->first_pin) / 8 ? EXAR_OFFSET_MPIOLVL_HI
> -                                                  : EXAR_OFFSET_MPIOLVL_LO;
> +       unsigned int pin = exar_gpio->first_pin + (offset % 16);
> +       unsigned int cascaded = offset / 16;
> +       unsigned int addr = pin / 8 ? EXAR_OFFSET_MPIOLVL_HI : EXAR_OFFSET_MPIOLVL_LO;
> +
> +       return addr + (cascaded ? exar_gpio->cascaded_offset : 0);
>  }
>
>  static unsigned int
>  exar_offset_to_bit(struct exar_gpio_chip *exar_gpio, unsigned int offset)
>  {
> -       return (offset + exar_gpio->first_pin) % 8;
> +       unsigned int pin = exar_gpio->first_pin + (offset % 16);
> +
> +       return pin % 8;
>  }
>
>  static int exar_get_direction(struct gpio_chip *chip, unsigned int offset)
> @@ -153,6 +172,17 @@ static int gpio_exar_probe(struct platform_device *pdev)
>         if (!exar_gpio)
>                 return -ENOMEM;
>
> +       /*
> +        * If cascaded, secondary xr17v354 or xr17v358 have the same amount
> +        * of MPIOs as their primaries and the last 4 bits of the primary's
> +        * PCI Device ID is the number of its UART channels.
> +        */
> +       if (pcidev->device & GENMASK(15, 12)) {
> +               ngpios += ngpios;
> +               exar_gpio->cascaded_offset = (pcidev->device & GENMASK(3, 0)) *
> +                               EXAR_UART_CHANNEL_SIZE;
> +       }
> +
>         /*
>          * We don't need to check the return values of mmio regmap operations (unless
>          * the regmap has a clock attached which is not the case here).
> --
> 2.34.1
>


-- 
With Best Regards,
Andy Shevchenko