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

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Date:   Thu, 16 Feb 2023 22:39:27 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Ben Dooks <ben.dooks@...ive.com>
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 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.

> 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.
 
Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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