linux-kernel - Re: [PATCH v6 10/10] pwm: dwc: use clock rate in hz to avoid rounding issues

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Message-ID: <9600a696-c3dd-acc5-3489-569c1590f224@sifive.com>
Date:   Thu, 10 Nov 2022 16:29:42 +0000
From:   Ben Dooks <ben.dooks@...ive.com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Greentime Hu <greentime.hu@...ive.com>,
        jarkko.nikula@...ux.intel.com,
        William Salmon <william.salmon@...ive.com>,
        Jude Onyenegecha <jude.onyenegecha@...ive.com>
Subject: Re: [PATCH v6 10/10] pwm: dwc: use clock rate in hz to avoid rounding
 issues

On 10/11/2022 15:42, Uwe Kleine-König wrote:
> Hello Ben,
> 
> On Thu, Oct 20, 2022 at 04:16:10PM +0100, Ben Dooks wrote:
>> As noted, the clock-rate when not a nice multiple of ns is probably
>> going to end up with inacurate caculations, as well as on a non pci
>> system the rate may change (although we've not put a clock rate
>> change notifier in this code yet) so we also add some quick checks
>> of the rate when we do any calculations with it.
>>
>> Signed-off-by; Ben Dooks <ben.dooks@...ive.com>
>> Reported-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
>> ---
>>   drivers/pwm/pwm-dwc-of.c |  2 +-
>>   drivers/pwm/pwm-dwc.c    | 29 ++++++++++++++++++++---------
>>   drivers/pwm/pwm-dwc.h    |  2 +-
>>   3 files changed, 22 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/pwm/pwm-dwc-of.c b/drivers/pwm/pwm-dwc-of.c
>> index c5b4351cc7b0..5f7f066859d4 100644
>> --- a/drivers/pwm/pwm-dwc-of.c
>> +++ b/drivers/pwm/pwm-dwc-of.c
>> @@ -50,7 +50,7 @@ static int dwc_pwm_plat_probe(struct platform_device *pdev)
>>   		return dev_err_probe(dev, PTR_ERR(dwc->clk),
>>   				     "failed to get timer clock\n");
>>   
>> -	dwc->clk_ns = NSEC_PER_SEC / clk_get_rate(dwc->clk);
>> +	dwc->clk_rate = clk_get_rate(dwc->clk);
> 
> Given that clk_ns is introduced only in this series, I suggest to make
> it right from the start.

I was trying to keep the splitting of the driver and the clock changes
separate to make any possible bisection easier.

-- 
Ben