linux-kernel - Re: [PATCH v16 2/2] pwm: airoha: Add support for EN7581 SoC

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Message-ID: <685ba7d9.df0a0220.e1b22.e6c2@mx.google.com>
Date: Wed, 25 Jun 2025 09:40:07 +0200
From: Christian Marangi <ansuelsmth@...il.com>
To: Uwe Kleine-König <ukleinek@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
	Andy Shevchenko <andriy.shevchenko@...el.com>,
	Benjamin Larsson <benjamin.larsson@...exis.eu>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>
Subject: Re: [PATCH v16 2/2] pwm: airoha: Add support for EN7581 SoC

On Wed, Jun 25, 2025 at 09:24:33AM +0200, Uwe Kleine-König wrote:
> Hello Christian,
> 
> On Wed, Jun 25, 2025 at 02:00:39AM +0200, Christian Marangi wrote:
> > +	/*
> > +	 * Period goes at 4ns step, normalize it to check if we can
> > +	 * share a generator.
> > +	 */
> > +	period_ns = rounddown_u64(period_ns, AIROHA_PWM_PERIOD_TICK_NS);
> 
> I don't understand why you need that. If you clamp to
> AIROHA_PWM_PERIOD_MAX_NS first, you don't need the (expensive) 64-bit
> operation. If you compare using ticks instead of ns you don't even need
> to round down, but just do the division that you end up doing anyhow.
> 

Correct me if I'm wrong but 

#define NSEC_PER_SEC	1000000000L
#define AIROHA_PWM_PERIOD_MAX_NS       (1 * NSEC_PER_SEC)

doesn't fit u32 so an u64 is needed.

And using ns until the apply process is handy for bucket sharing. I can
change it to reference ticks but I think the round is necessary.

You want to change everything to reference tick? (honestly this is a
good chance to introduce this missing API, since I feel also other might
benefits from this)

-- 
	Ansuel