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SubjectRe: [PATCH net-next RFC 3/9] net: dsa: mv88e6xxx: add support for GPIO configuration
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On 09/28/2017 08:25 AM, Brandon Streiff wrote:
> The Scratch/Misc register is a windowed interface that provides access
> to the GPIO configuration. Provide a new method for configuration of
> GPIO functions.
>
> Signed-off-by: Brandon Streiff <brandon.streiff@ni.com>
> ---

> +/* Offset 0x1A: Scratch and Misc. Register */
> +static int mv88e6xxx_g2_scratch_reg_read(struct mv88e6xxx_chip *chip,
> + int reg, u8 *data)
> +{
> + int err;
> + u16 value;
> +
> + err = mv88e6xxx_g2_write(chip, MV88E6XXX_G2_SCRATCH_MISC_MISC,
> + reg << 8);
> + if (err)
> + return err;
> +
> + err = mv88e6xxx_g2_read(chip, MV88E6XXX_G2_SCRATCH_MISC_MISC, &value);
> + if (err)
> + return err;
> +
> + *data = (value & MV88E6XXX_G2_SCRATCH_MISC_DATA_MASK);
> +
> + return 0;
> +}

With the write and read acquiring and then releasing the lock
immediately, is no there room for this sequence to be interrupted in the
middle and end-up returning inconsistent reads?

> +
> +static int mv88e6xxx_g2_scratch_reg_write(struct mv88e6xxx_chip *chip,
> + int reg, u8 data)
> +{
> + u16 value = (reg << 8) | data;
> +
> + return mv88e6xxx_g2_update(chip, MV88E6XXX_G2_SCRATCH_MISC_MISC, value);
> +}
> +
> +/* Configures the specified pin for the specified function. This function
> + * does not unset other pins configured for the same function. If multiple
> + * pins are configured for the same function, the lower-index pin gets
> + * that function and the higher-index pin goes back to being GPIO.
> + */
> +int mv88e6xxx_g2_set_gpio_config(struct mv88e6xxx_chip *chip, int pin,
> + int func, int dir)
> +{
> + int mode_reg = MV88E6XXX_G2_SCRATCH_GPIO_MODE(pin);
> + int dir_reg = MV88E6XXX_G2_SCRATCH_GPIO_DIR(pin);
> + int err;
> + u8 val;
> +
> + if (pin < 0 || pin >= mv88e6xxx_num_gpio(chip))
> + return -ERANGE;
> +
> + /* Set function first */
> + err = mv88e6xxx_g2_scratch_reg_read(chip, mode_reg, &val);
> + if (err)
> + return err;
> +
> + /* Zero bits in the field for this GPIO and OR in new config */
> + val &= ~MV88E6XXX_G2_SCRATCH_GPIO_MODE_MASK(pin);
> + val |= (func << MV88E6XXX_G2_SCRATCH_GPIO_MODE_OFFSET(pin));
> +
> + err = mv88e6xxx_g2_scratch_reg_write(chip, mode_reg, val);
> + if (err)
> + return err;
> +
> + /* Set direction */
> + err = mv88e6xxx_g2_scratch_reg_read(chip, dir_reg, &val);
> + if (err)
> + return err;
> +
> + /* Zero bits in the field for this GPIO and OR in new config */
> + val &= ~MV88E6XXX_G2_SCRATCH_GPIO_DIR_MASK(pin);
> + val |= (dir << MV88E6XXX_G2_SCRATCH_GPIO_DIR_OFFSET(pin));
> +
> + return mv88e6xxx_g2_scratch_reg_write(chip, dir_reg, val);
> +}

Would there be any value in implementing a proper gpiochip structure
here such that other pieces of SW can see this GPIO controller as a
provider and you can reference it from e.g: Device Tree using GPIO
descriptors?
--
Florian

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