Re: [PATCH v7 1/4] gpiolib: Pass bitmaps, not integer arrays, to get/set array

Geert Uytterhoeven
2018-09-03T14:24:33Z

On Mon, Sep 3, 2018 at 6:31 AM Matthew Wilcox <willy@infradead.org> wrote:
> > +++ b/drivers/auxdisplay/hd44780.c
> > @@ -62,17 +62,12 @@ 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;
> > -
> > - for (i = 0; i < 8; i++)
> > - values[PIN_DATA0 + i] = !!(val & BIT(i));
> > - values[PIN_CTRL_RS] = rs;
> > - n = 9;
> > - if (hd->pins[PIN_CTRL_RW]) {
> > - values[PIN_CTRL_RW] = 0;
> > - n++;
> > - }
> > + DECLARE_BITMAP(values, 10); /* for DATA[0-7], RS, RW */
> > + unsigned int n;
> > +
> > + *values = val;
> > + __assign_bit(8, values, rs);
> > + n = hd->pins[PIN_CTRL_RW] ? 10 : 9;
>
> Doesn't this assume little endian bitmaps? Has anyone tested this on
> big-endian machines?

include/linux/bitops.h:

static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
bool value)
{
if (value)
__set_bit(nr, addr);
else
__clear_bit(nr, addr);
}

include/asm-generic/bitops/non-atomic.h:

static inline void __set_bit(int nr, volatile unsigned long *addr)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);

*p |= mask;
}

include/linux/bits.h:

#define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG))

Looks like native endianness to me.

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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