Tiny delays in drivers/mtd/nand/nand_base.c
Mason
slash.tmp at free.fr
Wed Apr 1 09:40:17 PDT 2015
Hello everyone,
In drivers/mtd/nand/nand_base.c there are several instances of
the following code:
/*
* Apply this short delay always to ensure that we do wait tWB in
* any case on any machine.
*/
ndelay(100);
Is the intent to spin for 100 nanoseconds?
It seems that, for most platforms, ndelay is defined as:
udelay(DIV_ROUND_UP(x, 1000))
So it will resolve to udelay(1) if I understand correctly?
(I suppose sleeping longer is not a problem.)
However the comment implies that 100 ns are sufficient, right?
So if I override ndelay with a function that sleeps *exactly*
the amount requested, everything should keep working?
The reason I ask is because someone added this comment in my
source tree:
#ifdef CONFIG_TANGOX
udelay(1); /* needs to make it much longer than tWB */
#else
ndelay(100);
#endif
Also I have to figure out why the build is not picking up this
definition for ndelay (from include/asm-generic/delay.h)
/* 0x5 is 2**32 / 1000000000 (rounded up) */
#define ndelay(n) \
({ \
if (__builtin_constant_p(n)) { \
if ((n) / 20000 >= 1) \
__bad_ndelay(); \
else \
__const_udelay((n) * 5ul); \
} else { \
__ndelay(n); \
} \
})
Although it seems it should take HZ into account, as the argument
is then multiplied by ticks_per_jiffy (which is FREQ/HZ).
Regards.
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