From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Nikita Travkin <nikita@trvn.ru>
Cc: thierry.reding@gmail.com, lee.jones@linaro.org,
robh+dt@kernel.org, sboyd@kernel.org, krzk@kernel.org,
linus.walleij@linaro.org, masneyb@onstation.org,
sean.anderson@seco.com, linux-pwm@vger.kernel.org,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
~postmarketos/upstreaming@lists.sr.ht
Subject: Re: [PATCH v5 2/2] pwm: Add clock based PWM output driver
Date: Sat, 19 Feb 2022 11:10:49 +0100 [thread overview]
Message-ID: <20220219101049.erwzy5mpmsfgcwjy@pengutronix.de> (raw)
In-Reply-To: <425691dbe49115f04dbe89c158bf6d1c@trvn.ru>
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Hello,
On Sat, Feb 19, 2022 at 11:46:31AM +0500, Nikita Travkin wrote:
> Uwe Kleine-König писал(а) 14.02.2022 23:43:
> > On Sat, Feb 12, 2022 at 09:23:42PM +0500, Nikita Travkin wrote:
> >> + * Limitations:
> >> + * - Glitches are possible when new pwm state is applied.
> >> + * - Due to the fact that exact behavior depends on the underlying
> >> + * clock driver, various limitations are possible.
> >> + * - Period depends on the clock and, in general, not guaranteed.
> >
> > This sentence is broken.
> >
>
> Here what I mean is that the clock driver might e.g. have a lookup table
> for some rates and will only set one close to the requested ones.
> (Extreme scenario is that only one rate is allowed in the lookup table,
> which is a real possibility for some platforms that I think this driver
> will be used with, the lookup may need to be changed for those clocks)
>
> I will reword this like:
>
> Some clock drivers may only pick the closest available rate
> and not the exact requested one. Because of this, exact period
> is not guaranteed.
That there is no exact match is quite normal also for dedicated PWM
HW blocks. So I think the second item in your list is good enough to
cover the non-existing guaranteed for period and glitches.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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next prev parent reply other threads:[~2022-02-19 10:11 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-12 16:23 [PATCH v5 0/2] Clock based PWM output driver Nikita Travkin
2022-02-12 16:23 ` [PATCH v5 1/2] dt-bindings: pwm: Document clk based PWM controller Nikita Travkin
2022-02-14 7:43 ` Krzysztof Kozlowski
2022-02-12 16:23 ` [PATCH v5 2/2] pwm: Add clock based PWM output driver Nikita Travkin
2022-02-14 11:19 ` Krzysztof Kozlowski
2022-02-19 6:48 ` Nikita Travkin
2022-02-14 18:43 ` Uwe Kleine-König
2022-02-19 6:46 ` Nikita Travkin
2022-02-19 10:10 ` Uwe Kleine-König [this message]
2022-02-19 13:54 ` Nikita Travkin
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