diff options
| author | Uwe Kleine-König <u.kleine-koenig@pengutronix.de> | 2022-04-20 14:12:39 +0200 |
|---|---|---|
| committer | Thierry Reding <thierry.reding@gmail.com> | 2022-05-20 16:18:05 +0200 |
| commit | 3c173376efc461dc670b02ba2846c2a533491104 (patch) | |
| tree | cd48b75dfc3f01046d8b3096088dfdb96aab2526 /drivers/pwm/pwm-renesas-tpu.c | |
| parent | 208ab8676b9c787b4285364fcb52a159f94b861d (diff) | |
pwm: renesas-tpu: Improve maths to compute register settings
The newly computed register values are intended to exactly match the
previously computed values. The main improvement is that the prescaler
is computed without a loop that involves two divisions in each step.
This uses the fact, that prescalers[i] = 1 << (2 * i).
Assuming a moderately smart compiler, the needed number of divisions for
the case where the requested period is too big, is reduced from 5 to 2.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm/pwm-renesas-tpu.c')
| -rw-r--r-- | drivers/pwm/pwm-renesas-tpu.c | 50 |
1 files changed, 35 insertions, 15 deletions
diff --git a/drivers/pwm/pwm-renesas-tpu.c b/drivers/pwm/pwm-renesas-tpu.c index 5bced2050ece..4aff3870010c 100644 --- a/drivers/pwm/pwm-renesas-tpu.c +++ b/drivers/pwm/pwm-renesas-tpu.c @@ -244,7 +244,6 @@ static void tpu_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm) static int tpu_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, int duty_ns, int period_ns, bool enabled) { - static const unsigned int prescalers[] = { 1, 4, 16, 64 }; struct tpu_pwm_device *tpd = pwm_get_chip_data(pwm); struct tpu_device *tpu = to_tpu_device(chip); unsigned int prescaler; @@ -254,26 +253,47 @@ static int tpu_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, u32 duty; int ret; + clk_rate = clk_get_rate(tpu->clk); + + period = clk_rate / (NSEC_PER_SEC / period_ns); + /* - * Pick a prescaler to avoid overflowing the counter. - * TODO: Pick the highest acceptable prescaler. + * Find the minimal prescaler in [0..3] such that + * + * period >> (2 * prescaler) < 0x10000 + * + * This could be calculated using something like: + * + * prescaler = max(ilog2(period) / 2, 7) - 7; + * + * but given there are only four allowed results and that ilog2 isn't + * cheap on all platforms using a switch statement is more effective. */ - clk_rate = clk_get_rate(tpu->clk); + switch (period) { + case 1 ... 0xffff: + prescaler = 0; + break; - for (prescaler = 0; prescaler < ARRAY_SIZE(prescalers); ++prescaler) { - period = clk_rate / prescalers[prescaler] - / (NSEC_PER_SEC / period_ns); - if (period <= 0xffff) - break; - } + case 0x10000 ... 0x3ffff: + prescaler = 1; + break; - if (prescaler == ARRAY_SIZE(prescalers) || period == 0) { - dev_err(&tpu->pdev->dev, "clock rate mismatch\n"); - return -ENOTSUPP; + case 0x40000 ... 0xfffff: + prescaler = 2; + break; + + case 0x100000 ... 0x3fffff: + prescaler = 3; + break; + + default: + return -EINVAL; } + period >>= 2 * prescaler; + if (duty_ns) { - duty = clk_rate / prescalers[prescaler] + duty = (clk_rate >> 2 * prescaler) / (NSEC_PER_SEC / duty_ns); if (duty > period) return -EINVAL; @@ -283,7 +303,7 @@ static int tpu_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, dev_dbg(&tpu->pdev->dev, "rate %u, prescaler %u, period %u, duty %u\n", - clk_rate, prescalers[prescaler], period, duty); + clk_rate, 1 << (2 * prescaler), period, duty); if (tpd->prescaler == prescaler && tpd->period == period) duty_only = true; |