From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
"Rasmus Villemoes" <linux@rasmusvillemoes.dk>
Cc: devicetree@vger.kernel.org, linux-pwm@vger.kernel.org,
Shawn Guo <shawnguo@kernel.org>,
Sascha Hauer <s.hauer@pengutronix.de>,
linux-kernel@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
Thierry Reding <thierry.reding@gmail.com>,
NXP Linux Team <linux-imx@nxp.com>,
Pengutronix Kernel Team <kernel@pengutronix.de>,
Fabio Estevam <festevam@gmail.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 3/4] pwm: mxs: add support for inverse polarity
Date: Mon, 23 Sep 2019 10:45:56 +0200 [thread overview]
Message-ID: <d2b29144-3de8-4561-3292-49db7e697aca@rasmusvillemoes.dk> (raw)
In-Reply-To: <20190923082735.tzxyhvjlnztsxhsc@pengutronix.de>
On 23/09/2019 10.27, Uwe Kleine-König wrote:
> On Mon, Sep 23, 2019 at 10:13:47AM +0200, Rasmus Villemoes wrote:
>>
>>
>> + pol_bits = state->polarity == PWM_POLARITY_NORMAL ?
>> + PERIOD_POLARITY_NORMAL : PERIOD_POLARITY_INVERSE;
>> +
>> writel(duty_cycles << 16,
>> mxs->base + PWM_ACTIVE0 + pwm->hwpwm * 0x20);
>> - writel(PERIOD_PERIOD(period_cycles) | PERIOD_POLARITY_NORMAL | PERIOD_CDIV(div),
>> + writel(PERIOD_PERIOD(period_cycles) | pol_bits | PERIOD_CDIV(div),
>
> When will this affect the output? Only on the next start of a period, or
> immediatly? Can it happen that this results in a mixed output (i.e. a
> period that has already the new duty cycle from the line above but not
> the new polarity (or period)?
The data sheet says "Also, when the user reprograms the channel in this
manner, the new register values will not take effect until the beginning
of a new output period. This eliminates the potential for output
glitches that could occur if the registers were updated while the
channel was enabled and in the middle of a cycle.". So I think this
should be ok. "this manner" refers to the registers being written in the
proper order (first ACTIVEn, then PERIODn).
Rasmus
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next prev parent reply other threads:[~2019-09-23 8:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-23 8:13 [PATCH 0/4] pwm: mxs: add support for setting polarity via DT Rasmus Villemoes
2019-09-23 8:13 ` [PATCH 1/4] pwm: mxs: implement ->apply Rasmus Villemoes
2019-09-23 8:24 ` Uwe Kleine-König
2019-09-23 9:04 ` Rasmus Villemoes
2019-09-23 9:17 ` Uwe Kleine-König
2019-09-23 8:13 ` [PATCH 2/4] pwm: mxs: remove legacy methods Rasmus Villemoes
2019-09-23 8:13 ` [PATCH 3/4] pwm: mxs: add support for inverse polarity Rasmus Villemoes
2019-09-23 8:27 ` Uwe Kleine-König
2019-09-23 8:45 ` Rasmus Villemoes [this message]
2019-09-23 8:54 ` Uwe Kleine-König
2019-09-23 8:13 ` [PATCH 4/4] dt-bindings: pwm: mxs-pwm: Increase #pwm-cells Rasmus Villemoes
2019-10-02 14:19 ` Rob Herring
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