linux-kernel - Re: [PATCH v7 10/10] pwm: dwc: use clock rate in hz to avoid rounding issues

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Message-ID: <f993a71b-69ff-3047-9a56-d04fd583431a@sifive.com>
Date:   Wed, 14 Jun 2023 12:17:35 +0100
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 v7 10/10] pwm: dwc: use clock rate in hz to avoid rounding
 issues

On 16/02/2023 21:39, Uwe Kleine-König wrote:
> On Fri, Dec 23, 2022 at 03:38:20PM +0000, 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
> 
> Given that such a non-nice ca*l*culation only happens in the of case
> that is introduced here, it would be nice to move this patch before the
> introduction of the of-support.

I've moved of support to the end of the series
you
>> 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.
> 
> If the clk rate changes while the PWM is on, this modifies the output.
> This is unfortunate and so it justifies adding a call to
> clk_rate_exclusive_get() when the PWM is on.

I can't really test things any more as the hardware has been returned
to the client and I'm technically off the project (and awaiting this
email address to be closed down).

Could this either be solved by the clk_rate_exclusive_get() or adding
a clock change notifier? Either way I would prefer this to be work for
another patch.

I'll send v8 out later as it has had some re-works due to moving
things around.

Thank you for the review.

--
Ben