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Date:   Sat, 19 Feb 2022 11:10:49 +0100
From:   Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <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
Message-ID: <20220219101049.erwzy5mpmsfgcwjy@pengutronix.de>
References: <20220212162342.72646-1-nikita@trvn.ru>
 <20220212162342.72646-3-nikita@trvn.ru>
 <20220214184320.ym36pfvozwdp5nbb@pengutronix.de>
 <425691dbe49115f04dbe89c158bf6d1c@trvn.ru>
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Hello,

On Sat, Feb 19, 2022 at 11:46:31AM +0500, Nikita Travkin wrote:
> Uwe Kleine-K=C3=B6nig =D0=BF=D0=B8=D1=81=D0=B0=D0=BB(=D0=B0) 14.02.2022 2=
3:43:
> > 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.
> >=20
> > This sentence is broken.
> >=20
>=20
> 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)
>=20
> I will reword this like:
>=20
>   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

--=20
Pengutronix e.K.                           | Uwe Kleine-K=C3=B6nig         =
   |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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