[PATCH 2.6] I2C: New hardware monitoring driver: w83627ehf

Grant Coady grant_lkml at dodo.com.au
Sun Apr 17 00:26:51 CEST 2005


Hi Khali,
On Sat, 16 Apr 2005 23:00:13 +0200, Jean Delvare <khali at linux-fr.org> wrote:
>
>Good catch. I thought that the "if" clause was handling that case, but
>there is a small window (42 to 54 RPM or so) which will go through and
>actually result in an invalid divider (256), you're correct.

It is a very small window at low speed end, took me ages to work it 
out and find the special case when I lifted your code :)

>I also noticed that the "if" clause would fail to catch 41 RPM as it
>should, so I fixed it by using a less error-prone test.
>
>I now have:
>
>	if (!val) {
>		/* No min limit, alarm disabled */
>		data->fan_min[nr] = 255;
>		new_div = data->fan_div[nr]; /* No change */
>	} else if ((reg = 1350000U / val) >= 128 * 255) {
>		/* Speed below this value cannot possibly be represented,
>		   even with the highest divider (128) */
>		data->fan_min[nr] = 255;
>		new_div = 7; /* 128 == (1 << 7) */
>	} else {
>		/* Automatically pick the best divider, i.e. the one such
>		   that the min limit will correspond to a register value
>		   in the 96..192 range */
>		new_div = 0;
>		while (reg > 192 && new_div < 7) {
>			reg >>= 1;
>			new_div++;
>		}
>		data->fan_min[nr] = reg;
>	}
>
>Looks OK now?

Yes, but is the (!val) test needed?  I'd merge it with next test 
like so:
	if (val < 1350000U / (128 * 254)) {

as same end result is to store 255 to fan_min.

Cheers,
Grant.



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