Re: [PATCH 2/2] media: pwm-ir-tx: trigger edges from hrtimer interrupt context - Uwe Kleine-König

From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Sean Young <sean@mess.org>
Cc: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Thierry Reding <thierry.reding@gmail.com>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-pwm@vger.kernel.org
Subject: Re: [PATCH 2/2] media: pwm-ir-tx: trigger edges from hrtimer interrupt context
Date: Wed, 4 Oct 2023 11:35:58 +0200	[thread overview]
Message-ID: <20231004093558.bt7gf3m6erxxpaie@pengutronix.de> (raw)
In-Reply-To: <ZR0Xue8Mu8VZIxm5@gofer.mess.org>

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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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