On Tue, Apr 13, 2010 at 5:53 AM, Jamie Lokier <jamie@xxxxxxxxxxxxx> wrote: > Russell King - ARM Linux wrote: >> On Mon, Apr 12, 2010 at 09:32:35PM +0200, Jean Delvare wrote: >> > On Mon, 12 Apr 2010 20:20:10 +0100, Russell King - ARM Linux wrote: >> > > On Mon, Apr 12, 2010 at 09:13:19PM +0200, Jean Delvare wrote: >> > > > On Tue, 13 Apr 2010 01:57:51 +0800, Eric Miao wrote: >> > > > > One other better and cleaner approach to such inconsistency issue is >> > > > > to have a timeout_ms field, and having i2c-gpio.c driver to convert this >> > > > > to jiffies using msec_to_jiffies() at run-time. >> > > > >> > > > With what benefit? Expressing time values in units of HZ is very >> > > > frequent in the kernel code and shouldn't actually surprise anyone. >> > > >> > > Actually, this patch shows there is confusion. >> > > >> > > "Assume '100' means 100ms here and adapt accordingly." >> > > >> > > Since this patch is for ARM, where HZ=100, the above patch is not a >> > > simple "convert how we derive this constant" patch - it's a functional >> > > change, reducing the timeouts by a factor of 10. >> > > >> > > Could that be because the patch author misinterpreted the HZ-based >> > > values? >> > >> > I admit I would have assumed 100 -> HZ, as hard-coded HZ-dependent >> > value typically assume HZ=100. >> > >> > > I suspect I'm not the only one who thinks that the latter of "HZ / 10" >> > > "100ms" is easier to read and comprehend without mistake. >> > >> > OTOH, converting from ms to jiffies each time you need the value has a >> > cost. >> >> True; what I did for MMC stuff is converted it from ms to jiffies at >> initialization time when copying it in from platform data in the >> driver's probe function. >> >> I'm not saying that I care either way, I'm merely showing that dealing >> with HZ-based values can be (maybe unexpectedly) more error prone. > > HZ is used a lot in kernel timeouts, so even though it's confusing, it > is something everyone ought to get used to. I don't understand why people has to live with confusions where there is apparently a cleaner way to go. HZ is everywhere, and as long as they live within their own driver code, that's OK. > > But I agree it is too confusing. An obvious remedy is: > > #define milliseconds(ms) (((ms) * HZ + 999) / 1000) > #define seconds(s) ((s) * HZ) > This is to reinvent the wheel as there are already msecs_to_jiffies() and usecs_to_jiffies(), and vice versa. The only benefit of using macros instead of a function is for constants. This, however, can be worked around as Russell suggested. The additional run-time cost by this function, compared with a unit of jiffies, is insignificant. > -- Jamie > -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
