[PATCH net-next 09/12] gpio: tc956x: add TC956x/QPS615 support

[Linus Walleij]

Hi Alex,

thanks for your patch!

On Fri, May 1, 2026 at 5:55 PM Alex Elder <elder at riscstar.com> wrote:

> Toshiba TC956x is an Ethernet-AVB/TSN bridge and is essentially
> a small and highly-specialized SoC.  TC956x includes a GPIO block that
> can be accessed, alongside several other peripherals, via two PCIe
> endpoint functions.  The PCIe function driver creates an auxiliary
> device for the GPIO block, and that device gets bound to this auxiliary
> device driver.
>
> Co-developed-by: Daniel Thompson <daniel at riscstar.com>
> Signed-off-by: Daniel Thompson <daniel at riscstar.com>
> Signed-off-by: Alex Elder <elder at riscstar.com>
(...)

> +config GPIO_TC956X
> +       tristate "Toshiba TC956X GPIO support"
> +       depends on TOSHIBA_TC956X_PCI
> +       default m if TOSHIBA_TC956X_PCI

I think this driver can

select GPIO_REGMAP

> +#include <linux/auxiliary_bus.h>
> +#include <linux/dev_printk.h>
> +#include <linux/gpio/driver.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>

#include <linux/gpio/regmap.h>

> +#define TC956X_GPIO_COUNT      37      /* Number of GPIOs (20-21 reserved) */

I would just do 64 and flag > 37 as invalid.

> +/*
> + * struct tc956x_gpio - Information related to the embedded GPIO controller
> + * @chip:              GPIO chip structure
> + * @regmap:            MMIO register map for SFR GPIO region access
> + * @input_only:                Bitmap indicating which GPIOs are input-only
> + */
> +struct tc956x_gpio {
> +       struct gpio_chip chip;
> +       struct regmap *regmap;
> +       DECLARE_BITMAP(input_only, TC956X_GPIO_COUNT);

> +static int tc956x_gpio_get_direction(struct gpio_chip *gc, unsigned int offset)
> +static int tc956x_gpio_direction_input(struct gpio_chip *gc,
> +                                      unsigned int offset)
> +static int tc956x_gpio_direction_output(struct gpio_chip *gc,
> +                                       unsigned int offset, int value)
> +static int tc956x_gpio_get(struct gpio_chip *gc, unsigned int offset)
> +static int tc956x_gpio_set(struct gpio_chip *gc, unsigned int offset, int value)

REGMAP_GPIO can handle all of this for you with the right
parameterization, study the drivers using this already such as
those that appear when you type
git grep 'gpio\/regmap\.h'


> +static int tc956x_gpio_init_valid_mask(struct gpio_chip *gc,
> +                                      unsigned long *valid_mask,
> +                                      unsigned int ngpios)
> +{
> +       /*
> +        * GPIOs 2 and 3 are used by the PCI power control driver, and
> +        * we don't allow them to be used.  GPIOs 20 and 21 are reserved
> +        * (and not usable).
> +        */
> +       bitmap_fill(valid_mask, ngpios);
> +       bitmap_clear(valid_mask, 2, 2);
> +       bitmap_clear(valid_mask, 20, 2);
> +
> +       return 0;
> +}

That's good use of this facility.

I would say the chip has 64 lines and just
bitmap_clear(valid_mask, 37, 64 - 37);
but that's your pick. This probably works too.

> +       /* Mark GPIOs 22, 23, 24, 27, 28, 31, and 34 as input only */
> +       bitmap_set(gpio->input_only, 22, 3);
> +       bitmap_set(gpio->input_only, 27, 2);
> +       set_bit(31, gpio->input_only);
> +       set_bit(34, gpio->input_only);

regmap-gpio can't currently handle selective input-only or
output-only lines, but we can
very easily make it.

So I sent a patch for that (now in your inbox).

Check if this fixed_direction_sparse bitmap will do the trick
for you and provide Tested-by if it does, thanks!

Yours,
Linus Walleij