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

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Date:   Thu, 19 Sep 2019 13:11:15 +0200
From:   oUwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        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
Subject: Re: [PATCH] pwm: rockchip: simplify rockchip_pwm_get_state()

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.

As a side note: Is there publicly available documentation for this IP?
If a link were added to the driver's header we could check easily
ourselves.

Best regards
Uwe

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