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

On Mon, Sep 3, 2018 at 6:31 AM Matthew Wilcox [off-list ref] wrote:

quoted

+++ 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