linux-kernel - Re: [PATCH v8 4/5] pwm: kona: Add debug info to config function

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Message-ID: <557B4F3D.2000001@broadcom.com>
Date:	Fri, 12 Jun 2015 14:29:33 -0700
From:	Jonathan Richardson <jonathar@...adcom.com>
To:	Tim Kryger <tim.kryger@...il.com>
CC:	Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazau <anatol@...gle.com>,
	Arun Ramamurthy <arun.ramamurthy@...adcom.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Scott Branden <sbranden@...adcom.com>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	Linux PWM <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v8 4/5] pwm: kona: Add debug info to config function

On 15-05-30 09:42 AM, Tim Kryger wrote:
> On Tue, May 26, 2015 at 1:08 PM, Jonathan Richardson
> <jonathar@...adcom.com> wrote:
>> Adds debugging info to config function where duty cycle and period
>> are calculated and verified.
>>
>> Signed-off-by: Jonathan Richardson <jonathar@...adcom.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
>>

We can defer this for now until I can look into it further. It's not a
priority. I'm more concerned with core changes and kona pwm fix.

Thanks,
Jon


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