Re: [PATCH v5 1/4] gpiolib: Pass bitmaps, not integer arrays, to get/set array

From: Geert Uytterhoeven
Date: Thu Aug 30 2018 - 03:41:07 EST

Hi Janusz,

On Wed, Aug 29, 2018 at 10:48 PM Janusz Krzysztofik <jmkrzyszt@xxxxxxxxx> wrote:
> Most users of get/set array functions iterate consecutive bits of data,
> usually a single integer, while 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.
>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Miguel Ojeda Sandonis <miguel.ojeda.sandonis@xxxxxxxxx>
> Cc: Peter Korsgaard <peter.korsgaard@xxxxxxxxx>
> Cc: Peter Rosin <peda@xxxxxxxxxx>
> Cc: Andrew Lunn <andrew@xxxxxxx>
> Cc: Florian Fainelli <f.fainelli@xxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
> Cc: Kishon Vijay Abraham I <kishon@xxxxxx>
> Cc: Lars-Peter Clausen <lars@xxxxxxxxxx>
> Cc: Michael Hennerich <Michael.Hennerich@xxxxxxxxxx>
> Cc: Jonathan Cameron <jic23@xxxxxxxxxx>
> Cc: Hartmut Knaack <knaack.h@xxxxxx>
> Cc: Peter Meerwald-Stadler <pmeerw@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Jiri Slaby <jslaby@xxxxxxxx>
> Signed-off-by: Janusz Krzysztofik <jmkrzyszt@xxxxxxxxx>
> Acked-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>

Thanks for your patch!

> --- 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 */
> + 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);

The clearing is not needed, as this has been done by 'value_bitmap[0] = val;'

> n++;
> }

So the above block can be simplified to:

n = hd->pins[PIN_CTRL_RW] ? 10 : 9;

>
> /* 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 */

This comment is not correct, as the low bits will be used.

/* DATA[4-7], RS, RW */

> + unsigned long value_bitmap[1];
> + 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);

Not needed.

> n++;
> }

Hence:

n = hd->pins[PIN_CTRL_RW] ? 6: 5;

> + value_bitmap[0] >>= PIN_DATA4;

Yuck?!?

Isn't it more readable to just do:

/* High nibble + RS, RW */
value_bitmap[0] = val >> 4;
__assign_bit(4, value_bitmap, rs);
n = hd->pins[PIN_CTRL_RW] ? 6: 5;

>
> /* 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);

... and:

/* Low nibble */
value_bitmap[0] &= ~0x0f;
value_bitmap[0] |= val & 0x0f;

>
> /* 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);
> }
> @@ -155,23 +153,23 @@ static void hd44780_write_cmd_gpio4(struct charlcd *lcd, int cmd)
> /* Send 4-bits of a command to the LCD panel in raw 4 bit GPIO mode */
> static void hd44780_write_cmd_raw_gpio4(struct charlcd *lcd, int cmd)
> {
> - int values[10]; /* for DATA[0-7], RS, RW, but DATA[0-3] is unused */
> + /* for DATA[0-7], RS, RW, but DATA[0-3] is unused */

This comment is not correct, as the low bits will be used.

/* DATA[4-7], RS, RW */

> + unsigned long value_bitmap[1];
> struct hd44780 *hd = lcd->drvdata;
> - unsigned int i, n;
> + unsigned int n;
>
> /* Command nibble + RS, RW */
> - for (i = 0; i < 4; i++)
> - values[PIN_DATA4 + i] = !!(cmd & BIT(i));
> - values[PIN_CTRL_RS] = 0;
> + value_bitmap[0] = cmd << PIN_DATA4;
> + __clear_bit(PIN_CTRL_RS, value_bitmap);

Implied by the assignment above.

> 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;

Hence:

/* Command nibble + RS, RW */
value_bitmap[0] = cmd;
n = hd->pins[PIN_CTRL_RW] ? 6: 5;


>
> /* 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);
> }

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds