linux-kernel - Re: [PATCH] gpio: 74x164: Implement gpiochip.set

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Date:	Tue, 15 Mar 2016 12:04:17 +0800
From:	Phil Reid <preid@...ctromag.com.au>
To:	Geert Uytterhoeven <geert+renesas@...der.be>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Gabor Juhos <juhosg@...nwrt.org>,
	Miguel Gaio <miguel.gaio@...xo.com>
Cc:	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpio: 74x164: Implement gpiochip.set_multiple()

On 14/03/2016 11:19 PM, Geert Uytterhoeven wrote:
> This allows to set multiple outputs using a single SPI transfer.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>

Reviewed-by: Phil Reid <preid@...ctromag.com.au>


I do have a general question about GPIO drivers.
pca953x does not update the cached data unless the write operation
was successful. Which I folowed with the implement of set_multiple.
However a number of other drivers update regardless.
eg chip->buffer is updated even if the write_config fails.

What is the preferred approach?

> ---
>   drivers/gpio/gpio-74x164.c | 24 ++++++++++++++++++++++++
>   1 file changed, 24 insertions(+)
>
> diff --git a/drivers/gpio/gpio-74x164.c b/drivers/gpio/gpio-74x164.c
> index c81224ff2dca988b..62291a81c97f7140 100644
> --- a/drivers/gpio/gpio-74x164.c
> +++ b/drivers/gpio/gpio-74x164.c
> @@ -75,6 +75,29 @@ static void gen_74x164_set_value(struct gpio_chip *gc,
>   	mutex_unlock(&chip->lock);
>   }
>
> +static void gen_74x164_set_multiple(struct gpio_chip *gc, unsigned long *mask,
> +				    unsigned long *bits)
> +{
> +	struct gen_74x164_chip *chip = gpiochip_get_data(gc);
> +	unsigned int i, idx, shift;
> +	u8 bank, bankmask;
> +
> +	mutex_lock(&chip->lock);
> +	for (i = 0, bank = chip->registers - 1; i < chip->registers;
> +	     i++, bank--) {
> +		idx = i / sizeof(*mask);
> +		shift = i % sizeof(*mask) * BITS_PER_BYTE;
> +		bankmask = mask[idx] >> shift;
> +		if (!bankmask)
> +			continue;
> +
> +		chip->buffer[bank] &= ~bankmask;
> +		chip->buffer[bank] |= bankmask & (bits[idx] >> shift);
> +	}
> +	__gen_74x164_write_config(chip);
> +	mutex_unlock(&chip->lock);
> +}
> +
>   static int gen_74x164_direction_output(struct gpio_chip *gc,
>   		unsigned offset, int val)
>   {
> @@ -114,6 +137,7 @@ static int gen_74x164_probe(struct spi_device *spi)
>   	chip->gpio_chip.direction_output = gen_74x164_direction_output;
>   	chip->gpio_chip.get = gen_74x164_get_value;
>   	chip->gpio_chip.set = gen_74x164_set_value;
> +	chip->gpio_chip.set_multiple = gen_74x164_set_multiple;
>   	chip->gpio_chip.base = -1;
>
>   	chip->registers = nregs;
>


-- 
Regards
Phil Reid