[PATCH 4/4] gpio: aspeed: Add interfaces for co-processor to grab GPIOs

[Joel Stanley]

On 12 June 2018 at 09:40, Benjamin Herrenschmidt
<benh at kernel.crashing.org> wrote:
> On the Aspeed chip, the GPIOs can be under control of the ARM
> chip or of the ColdFire coprocessor. (There's a third command
> source, the LPC bus, which we don't use or support yet).
>
> The control of which master is allowed to modify a given
> GPIO is per-bank (8 GPIOs).
>
> Unfortunately, systems already exist for which we want to
> use GPIOs of both sources in the same bank.
>
> This provides an API exported by the gpio-aspeed driver
> that an aspeed coprocessor driver can use to "grab" some
> GPIOs for use by the coprocessor, and allow the coprocessor
> driver to provide callbacks for arbitrating access.
>
> Once at least one GPIO of a given bank has been "grabbed"
> by the coprocessor, the entire bank is marked as being
> under coprocessor control. It's command source is switched
> to the coprocessor.
>
> If the ARM then tries to write to a GPIO in such a marked bank,
> the provided callbacks are used to request access from the
> coprocessor driver, which is responsible to doing whatever
> is necessary to "pause" the coprocessor or prevent it from
> trying to use the GPIOs while the ARM is doing its accesses.
>
> During that time, the command source for the bank is temporarily
> switched back to the ARM.
>
> Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>

Looks okay to me. Just need to deal with the memory allocated.

> +
> +/**
> + * aspeed_gpio_copro_grab_gpio - Mark a GPIO used by the coprocessor. The entire
> + *                               bank gets marked and any access from the ARM will
> + *                               result in handshaking via callbacks.
> + * @desc: The GPIO to be marked
> + */
> +int aspeed_gpio_copro_grab_gpio(struct gpio_desc *desc)
> +{
> +       struct gpio_chip *chip = gpiod_to_chip(desc);
> +       struct aspeed_gpio *gpio = gpiochip_get_data(chip);
> +       int rc = 0, bindex, offset = gpio_chip_hwgpio(desc);
> +       const struct aspeed_gpio_bank *bank = to_bank(offset);
> +       unsigned long flags;
> +
> +       if (!gpio->cf_copro_bankmap)
> +               gpio->cf_copro_bankmap = kzalloc(gpio->config->nr_gpios >> 3, GFP_KERNEL);

Someone should free this.

> +       if (!gpio->cf_copro_bankmap)
> +               return -ENOMEM;
> +       if (offset < 0 || offset > gpio->config->nr_gpios)
> +               return -EINVAL;
> +       bindex = offset >> 3;
> +
> +       spin_lock_irqsave(&gpio->lock, flags);
> +
> +       /* Sanity check, this shouldn't happen */
> +       if (gpio->cf_copro_bankmap[bindex] == 0xff) {
> +               rc = -EIO;
> +               goto bail;
> +       }
> +       gpio->cf_copro_bankmap[bindex]++;
> +
> +       /* Switch command source */
> +       if (gpio->cf_copro_bankmap[bindex] == 1)
> +               aspeed_gpio_change_cmd_source(gpio, bank, bindex,
> +                                             GPIO_CMDSRC_COLDFIRE);
> +
> + bail:
> +       spin_unlock_irqrestore(&gpio->lock, flags);
> +       return rc;
> +}
> +EXPORT_SYMBOL_GPL(aspeed_gpio_copro_grab_gpio);