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SubjectRe: [PATCH v8 4/5] pwm: kona: Add debug info to config function
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On Tue, May 26, 2015 at 1:08 PM, Jonathan Richardson
<jonathar@broadcom.com> wrote:
> Adds debugging info to config function where duty cycle and period
> are calculated and verified.
>
> Signed-off-by: Jonathan Richardson <jonathar@broadcom.com>
> ---
> drivers/pwm/pwm-bcm-kona.c | 25 +++++++++++++++++++++++--
> 1 file changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pwm/pwm-bcm-kona.c b/drivers/pwm/pwm-bcm-kona.c
> index c87621f..0ddf19b 100644
> --- a/drivers/pwm/pwm-bcm-kona.c
> +++ b/drivers/pwm/pwm-bcm-kona.c
> @@ -138,18 +138,39 @@ static int kona_pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm,
> dc = div64_u64(val, div);
>
> /* If duty_ns or period_ns are not achievable then return */
> - if (pc < PERIOD_COUNT_MIN || dc < DUTY_CYCLE_HIGH_MIN)

The original code was based on the SPEAr PWM driver which has a non-zero
PWMDCR_MIN_DUTY such that the second condition here can evaluate to true.

This isn't the case for the Kona PWM where DUTY_CYCLE_HIGH_MIN is zero.

> + if (pc < PERIOD_COUNT_MIN) {
> + dev_warn(chip->dev,
> + "%s: pwm[%d]: period=%d is not achievable, pc=%lu, prescale=%lu\n",
> + __func__, chan, period_ns, pc, prescale);
> return -EINVAL;
> + }

Why not just print the minimum allowable period with the provided clock?

I don't think pc and prescale will be particularly helpful to users.

Also, do we really need to print __func__ here?

> +
> + if (dc < DUTY_CYCLE_HIGH_MIN) {
> + if (0 != duty_ns) {
> + dev_warn(chip->dev,
> + "%s: pwm[%d]: duty cycle=%d is not achievable, dc=%lu, prescale=%lu\n",
> + __func__, chan, duty_ns, dc, prescale);
> + }
> + return -EINVAL;
> + }

The above block is unreachable code.

>
> /* If pc and dc are in bounds, the calculation is done */
> if (pc <= PERIOD_COUNT_MAX && dc <= DUTY_CYCLE_HIGH_MAX)
> break;
>
> /* Otherwise, increase prescale and recalculate pc and dc */
> - if (++prescale > PRESCALE_MAX)
> + if (++prescale > PRESCALE_MAX) {
> + dev_warn(chip->dev,
> + "%s: pwm[%d]: Prescale (=%lu) within max (=%d) for period=%d and duty cycle=%d is not achievable\n",
> + __func__, chan, prescale, PRESCALE_MAX,
> + period_ns, duty_ns);
> return -EINVAL;
> + }
> }

The user got here because they specified a period larger than the maximum
supported so why not tell them largest value that can be supported instead
of confusing them with prescale and PRESCALE_MAX?

>
> + dev_dbg(chip->dev, "pwm[%d]: period=%lu, duty_high=%lu, prescale=%lu\n",
> + chan, pc, dc, prescale);
> +

This could be more clear. It prints pc but calls it period.

> /*
> * Don't apply settings if disabled. The period and duty cycle are
> * always calculated above to ensure the new values are
> --
> 1.7.9.5
>


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