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SubjectRe: [PATCH v2 5/8] mtd: maps: gpio-addr-flash: Replace array with an integer
On Wed,  5 Sep 2018 16:36:40 +0200
Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com> wrote:

> By replacing the array with an integer we can avoid completely
> the bit comparison loop if the value has not changed (by far
> the most common case).
>
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
> ---
> drivers/mtd/maps/gpio-addr-flash.c | 31 +++++++++++++++---------------
> 1 file changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/mtd/maps/gpio-addr-flash.c b/drivers/mtd/maps/gpio-addr-flash.c
> index 22e100f07112..8f5e3dce9be3 100644
> --- a/drivers/mtd/maps/gpio-addr-flash.c
> +++ b/drivers/mtd/maps/gpio-addr-flash.c
> @@ -43,7 +43,7 @@ struct async_state {
> struct map_info map;
> size_t gpio_count;
> unsigned *gpio_addrs;
> - int *gpio_values;
> + unsigned int gpio_values;
> unsigned int win_order;
> };
> #define gf_map_info_to_state(mi) ((struct async_state *)(mi)->map_priv_1)
> @@ -55,22 +55,25 @@ struct async_state {
> *
> * Rather than call the GPIO framework every time, cache the last-programmed
> * value. This speeds up sequential accesses (which are by far the most common
> - * type). We rely on the GPIO framework to treat non-zero value as high so
> - * that we don't have to normalize the bits.
> + * type).
> */
> static void gf_set_gpios(struct async_state *state, unsigned long ofs)
> {
> - size_t i = 0;
> - int value;
> + int i;
>
> ofs >>= state->win_order;
> - do {
> - value = ofs & (1 << i);
> - if (state->gpio_values[i] != value) {
> - gpio_set_value(state->gpio_addrs[i], value);
> - state->gpio_values[i] = value;
> - }
> - } while (++i < state->gpio_count);
> +
> + if (ofs == state->gpio_values)
> + return;
> +
> + for (i = 0; i < state->gpio_count; i++) {
> + if ((ofs & BIT(i)) == (state->gpio_values & BIT(i)))

Parens around the xx & BIT(i) operations are unneeded.

> + continue;
> +
> + gpio_set_value(state->gpio_addrs[i], !!(ofs & BIT(i)));
> + }
> +
> + state->gpio_values = ofs;
> }
>
> /**
> @@ -215,7 +218,7 @@ static int gpio_flash_probe(struct platform_device *pdev)
> if (!memory || !gpios || !gpios->end)
> return -EINVAL;
>
> - arr_size = sizeof(int) * gpios->end;
> + arr_size = sizeof(state->gpio_addrs[0]) * gpios->end;
> state = devm_kzalloc(&pdev->dev, sizeof(*state) + arr_size, GFP_KERNEL);
> if (!state)
> return -ENOMEM;
> @@ -226,9 +229,7 @@ static int gpio_flash_probe(struct platform_device *pdev)
> */
> state->gpio_count = gpios->end;
> state->gpio_addrs = (void *)(unsigned long)gpios->start;
> - state->gpio_values = (void *)(state + 1);
> state->win_order = get_bitmask_order(resource_size(memory)) - 1;
> - memset(state->gpio_values, 0xff, arr_size);
>
> state->map.name = DRIVER_NAME;
> state->map.read = gf_read;

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