linux-kernel - Re: [PATCH] pwm: rockchip: simplify rockchip_pwm_get

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Message-ID: <20200523200125.khdw3eau5eakxqy6@pengutronix.de>
Date:   Sat, 23 May 2020 22:01:25 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     David Wu <david.wu@...k-chips.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Heiko Stuebner <heiko@...ech.de>, linux-pwm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH] pwm: rockchip: simplify rockchip_pwm_get_state()

Hello David,

On Thu, Sep 19, 2019 at 01:11:15PM +0200, oUwe Kleine-König wrote:
> On Thu, Sep 19, 2019 at 11:17:27AM +0200, Rasmus Villemoes wrote:
> > The way state->enabled is computed is rather convoluted and hard to
> > read - both branches of the if() actually do the exact same thing. So
> > remove the if(), and further simplify "<boolean condition> ? true :
> > false" to "<boolean condition>".
> > 
> > Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> > ---
> > I stumbled on this while trying to understand how the pwm subsystem
> > works. This patch is a semantic no-op, but it's also possible that,
> > say, the first branch simply contains a "double negative" so either
> > the != should be == or the "false : true" should be "true : false".
> 
> The change looks obviously right, it's a noop.
> 
> I share your doubts however. The construct was introduced in commit 
> 831b2790507b ("pwm: rockchip: Use same PWM ops for each IP") by David
> Wu.
> 
> Before there were rockchip_pwm_get_state_v1 for the supports_polarity =
> false case and rockchip_pwm_get_state_v2 for supports_polarity = true.
> 
> In both state->enabled was assigned true if ((val & enable_conf) ==
> enable_conf). So I assume everything is fine.
> 
> A confirmation by David would be great though.

This is still open. Can you please have a look at
https://patchwork.ozlabs.org/project/linux-pwm/patch/20190919091728.24756-1-linux@rasmusvillemoes.dk/
and verify it's correct?

Best regards
Uwe

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