On Thu, Jun 18, 2015 at 09:58:59PM +0800, Yingjoe Chen wrote:

On Thu, 2015-06-18 at 18:19 +0800, YH Huang wrote:

quoted

On Fri, 2015-06-12 at 12:20 +0200, Thierry Reding wrote:

quoted

quoted

+/* Shift log2(PWM_PERIOD_MAX + 1) as divisor */
+#define PWM_PERIOD_BIT_SHIFT	12

I wasn't very clear about this in my earlier review, so let me try to
explain why I think this is confusing. You use this as a divisor, but
you encode it as a shift. It's also PWM_PERIOD_MAX + 1, so I think it
would make more sense to drop this, keep PWM_PERIOD_MAX as above and
then replace the

	>> PWM_PERIOD_BIT_SHIFT
	
below by

	/ (PWM_PERIOD_MAX + 1)

Maybe I can change in this way:
Remove this: #define PWM_PERIOD_MAX		0x00000fff
Using ">> PWM_PERIOD_BIT_SHIFT" is faster than "/ (PWM_PERIOD_MAX + 1)"
Is this right?

The place which use this shift is:

	clk_div = div_u64(rate * period_ns, NSEC_PER_SEC) >> 
			  PWM_PERIOD_BIT_SHIFT;

div_u64 return u64. If we change >> to /, and somehow compiler didn't
optimize that div into shift, it will cause build error.

Good point. I think every compiler should be able to optimize this, but
the shift isn't any worse than a divide and if we can proactively avoid
portability issues, let's go with the shift.

Thierry
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