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| author | Laxman Dewangan <ldewangan@nvidia.com> | 2017-04-07 15:04:00 +0530 |
|---|---|---|
| committer | Thierry Reding <thierry.reding@gmail.com> | 2017-04-12 16:08:15 +0200 |
| commit | 250b76f43f57d578ebff5e7211eb2c73aa5cd6ca (patch) | |
| tree | e0635c1349f94e77e02ade5103052124b7d75f5e /Documentation/DMA-attributes.txt | |
| parent | 90241fb9b55a36edd9dafb8de679f66836e84369 (diff) | |
| download | linux-250b76f43f57d578ebff5e7211eb2c73aa5cd6ca.tar.bz2 | |
pwm: tegra: Increase precision in PWM rate calculation
The rate of the PWM calculated as follows:
hz = NSEC_PER_SEC / period_ns;
rate = (rate + (hz / 2)) / hz;
This has the precision loss in lower PWM rate.
Change this to have more precision as:
hz = DIV_ROUND_CLOSEST_ULL(NSEC_PER_SEC * 100, period_ns);
rate = DIV_ROUND_CLOSEST(rate * 100, hz)
Example:
1. period_ns = 16672000, PWM clock rate is 200 KHz.
Based on old formula
hz = NSEC_PER_SEC / period_ns
= 1000000000ul/16672000
= 59 (59.98)
rate = (200K + 59/2)/59 = 3390
Based on new method:
hz = 5998
rate = DIV_ROUND_CLOSE(200000*100, 5998) = 3334
If we measure the PWM signal rate, we will get more accurate
period with rate value of 3334 instead of 3390.
2. period_ns = 16803898, PWM clock rate is 200 KHz.
Based on old formula:
hz = 59, rate = 3390
Based on new formula:
hz = 5951, rate = 3360
The PWM signal rate of 3360 is more near to requested period
than 3333.
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'Documentation/DMA-attributes.txt')
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