linux-kernel - Re: [PATCH 2/2] media: pwm-ir-tx: trigger edges from hrtimer interrupt context

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Date:   Wed, 4 Oct 2023 11:35:58 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Sean Young <sean@...s.org>
Cc:     Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org
Subject: Re: [PATCH 2/2] media: pwm-ir-tx: trigger edges from hrtimer
 interrupt context

Hello,

On Wed, Oct 04, 2023 at 08:43:53AM +0100, Sean Young wrote:
> On Mon, Oct 02, 2023 at 12:52:00PM +0300, Ivaylo Dimitrov wrote:
> > On 2.10.23 г. 11:20 ч., Sean Young wrote:
> > > Requires a copy of pwm_state in pwm_ir, not a huge difference (copy of 28
> > > bytes vs keeping it around).
> > 
> > see my previous comment re struct var. Also, look at the overhead:
> > https://elixir.bootlin.com/linux/v6.6-rc3/source/include/linux/pwm.h#L349 -
> > you call pwm_get_state() for every edge.
> 
> That's the 28 bytes copy I was talking about.

Note that pwm_get_state() also has (IMHO) confusing semantics. It gives
you (most of the time) the state that was last pwm_state_apply()d and
not the state the hardware is currently in. In my book keeping the
pwm_state around is the nicer approach that often is also simpler ...

> However keeping a pointer in struct pwm_ir is a good compromise and makes
> the rest of the code cleaner.

... which seems to apply here, too.

Best regards
Uwe

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

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