linux-kernel - Re: [PATCH] media: gpio-ir-tx: Driver does not behave with PREEMPT

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Message-ID: <20241002134843.rFHJYxSI@linutronix.de>
Date: Wed, 2 Oct 2024 15:48:43 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Sean Young <sean@...s.org>
Cc: linux-media@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: gpio-ir-tx: Driver does not behave with PREEMPT_RT

On 2024-09-21 20:07:20 [+0100], Sean Young wrote:
> This driver bit-bangs a signal with interrupts disabled. The signal can
> last for up to half a second (IR_MAX_DURATION).
> 
> A much better way of transmitting IR is using the pwm-ir-tx driver,
> which does not disable interrupts.

If you have to spin to make the signal exact and there is no other way
then be may guest.

Acked-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

But RT or not, spinning for up to 0.5s is a lot. Is this 0.5s in total
or 0.5 * count?
Anyway, gpio_ir_tx_unmodulated() and gpio_ir_tx_modulated() have
local_irq_disable() in there which can be removed. It got introduced in
commit 1451b93223bbe ("media: gpio-ir-tx: spinlock is not needed to
disable interrupts") but the previous irq-save is enough.

> Signed-off-by: Sean Young <sean@...s.org>

Sebastian