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SubjectRe: [RFC RFT PATCH v4 1/4] gpiolib: Pass bitmaps, not integer arrays, to get/set array
Hi Janusz,

On Tue, Aug 21, 2018 at 1:43 AM, Janusz Krzysztofik <jmkrzyszt@gmail.com> wrote:
> Most users of get/set array functions iterate consecutive bits of data,
> usually a single integer, while or processing array of results obtained
> from or building an array of values to be passed to those functions.
> Save time wasted on those iterations by changing the functions' API to
> accept bitmaps.
>
> All current users are updated as well.
>
> More benefits from the change are expected as soon as planned support
> for accepting/passing those bitmaps directly from/to respective GPIO
> chip callbacks if applicable is implemented.
>
> Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
> ---
> Documentation/driver-api/gpio/consumer.rst | 22 ++++----
> drivers/auxdisplay/hd44780.c | 52 +++++++++--------

[CC'ing Willy and Geert for hd44780]

> diff --git a/drivers/auxdisplay/hd44780.c b/drivers/auxdisplay/hd44780.c
> index f1a42f0f1ded..d340473aa142 100644
> --- a/drivers/auxdisplay/hd44780.c
> +++ b/drivers/auxdisplay/hd44780.c
> @@ -62,20 +62,19 @@ static void hd44780_strobe_gpio(struct hd44780 *hd)
> /* write to an LCD panel register in 8 bit GPIO mode */
> static void hd44780_write_gpio8(struct hd44780 *hd, u8 val, unsigned int rs)
> {
> - int values[10]; /* for DATA[0-7], RS, RW */
> - unsigned int i, n;
> + unsigned long value_bitmap[1]; /* for DATA[0-7], RS, RW */

Why [1]? I understand it is because in other cases it may be more than
one, but...

> + unsigned int n;
>
> - for (i = 0; i < 8; i++)
> - values[PIN_DATA0 + i] = !!(val & BIT(i));
> - values[PIN_CTRL_RS] = rs;
> + value_bitmap[0] = val;
> + __assign_bit(PIN_CTRL_RS, value_bitmap, rs);
> n = 9;
> if (hd->pins[PIN_CTRL_RW]) {
> - values[PIN_CTRL_RW] = 0;
> + __clear_bit(PIN_CTRL_RW, value_bitmap);
> n++;
> }
>
> /* Present the data to the port */
> - gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA0], values);
> + gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA0], value_bitmap);
>
> hd44780_strobe_gpio(hd);
> }
> @@ -83,32 +82,31 @@ static void hd44780_write_gpio8(struct hd44780 *hd, u8 val, unsigned int rs)
> /* write to an LCD panel register in 4 bit GPIO mode */
> static void hd44780_write_gpio4(struct hd44780 *hd, u8 val, unsigned int rs)
> {
> - int values[10]; /* for DATA[0-7], RS, RW, but DATA[0-3] is unused */
> - unsigned int i, n;
> + /* for DATA[0-7], RS, RW, but DATA[0-3] is unused */
> + unsigned long value_bitmap[0];

This one is even more strange... :-)

> + unsigned int n;
>
> /* High nibble + RS, RW */
> - for (i = 4; i < 8; i++)
> - values[PIN_DATA0 + i] = !!(val & BIT(i));
> - values[PIN_CTRL_RS] = rs;
> + value_bitmap[0] = val;
> + __assign_bit(PIN_CTRL_RS, value_bitmap, rs);
> n = 5;
> if (hd->pins[PIN_CTRL_RW]) {
> - values[PIN_CTRL_RW] = 0;
> + __clear_bit(PIN_CTRL_RW, value_bitmap);
> n++;
> }
> + value_bitmap[0] = value_bitmap[0] >> PIN_DATA4;

Maybe >>=?

>
> /* Present the data to the port */
> - gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA4],
> - &values[PIN_DATA4]);
> + gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA4], value_bitmap);
>
> hd44780_strobe_gpio(hd);
>
> /* Low nibble */
> - for (i = 0; i < 4; i++)
> - values[PIN_DATA4 + i] = !!(val & BIT(i));
> + value_bitmap[0] &= ~((1 << PIN_DATA4) - 1);
> + value_bitmap[0] |= val & ~((1 << PIN_DATA4) - 1);

Are you sure this is correct? You are basically doing an or of
value_bitmap and val and clearing the low-nibble.

>
> /* Present the data to the port */
> - gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA4],
> - &values[PIN_DATA4]);
> + gpiod_set_array_value_cansleep(n, &hd->pins[PIN_DATA4], value_bitmap);
>
> hd44780_strobe_gpio(hd);
> }

Cheers,
Miguel

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