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Date:   Fri, 16 Jul 2021 09:09:43 +0200
From:   Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To:     Billy Tsai <billy_tsai@aspeedtech.com>
Cc:     "lee.jones@linaro.org" <lee.jones@linaro.org>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "joel@jms.id.au" <joel@jms.id.au>,
        "andrew@aj.id.au" <andrew@aj.id.au>,
        "thierry.reding@gmail.com" <thierry.reding@gmail.com>,
        "p.zabel@pengutronix.de" <p.zabel@pengutronix.de>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-aspeed@lists.ozlabs.org" <linux-aspeed@lists.ozlabs.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
        BMC-SW <BMC-SW@aspeedtech.com>
Subject: Re: [v9 2/2] pwm: Add Aspeed ast2600 PWM support
Message-ID: <20210716070943.ayxkz2irkwhgincz@pengutronix.de>
References: <20210709065217.6153-1-billy_tsai@aspeedtech.com>
 <20210709065217.6153-3-billy_tsai@aspeedtech.com>
 <20210715150533.vppkw5oiomkxmfrn@pengutronix.de>
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Hello Billy,

On Fri, Jul 16, 2021 at 01:48:20AM +0000, Billy Tsai wrote:
> On 2021/7/15, 11:06 PM, "Uwe Kleine-K=F6nig" <u.kleine-koenig@pengutronix=
=2Ede>> wrote:
>     > Another is: The PWM doesn't support duty_cycle 0, on such a request=
 the
>     > PWM is disabled which results in a constant inactive level.
>=20
>     > (This is correct, is it? Or does it yield a constant 0 level?)
>=20
> Our pwm can support duty_cycle 0 by unset CLK_ENABLE.

This has a slightly different semantic though. Some consumer might
expect that the following sequence:

	pwm_apply(mypwm, { .period =3D 10000, .duty_cycle =3D 10000, .enabled =3D =
true })
	pwm_apply(mypwm, { .period =3D 10000, .duty_cycle =3D 0, .enabled =3D true=
 })
	pwm_apply(mypwm, { .period =3D 10000, .duty_cycle =3D 10000, .enabled =3D =
true })

results in the output being low for an integer multiple of 10 =B5s. This
isn't given with setting CLK_ENABLE to zero, is it? (I didn't recheck,
if the PWM doesn't complete periods on reconfiguration this doesn't
matter much though.)

Best regards
Uwe

--=20
Pengutronix e.K.                           | Uwe Kleine-K=F6nig            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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