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From: Sean Young <sean@mess.org>
To: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Cc: linux-media@vger.kernel.org, "Tony Lindgren" <tony@atomide.com>,
	"Russell King" <linux@armlinux.org.uk>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Timo Kokkonen" <timo.t.kokkonen@iki.fi>,
	"Pali Rohár" <pali.rohar@gmail.com>,
	"Sicelo A . Mhlongo" <absicsz@gmail.com>,
	linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org
Subject: Re: [PATCH v5 2/2] media: rc: remove ir-rx51 in favour of generic pwm-ir-tx
Date: Tue, 26 Sep 2023 08:16:33 +0100	[thread overview]
Message-ID: <ZRKFUb1vRtn82bgn@gofer.mess.org> (raw)
In-Reply-To: <99f0042f-538c-bcaf-96fd-bac24a87f88e@gmail.com>

On Mon, Sep 25, 2023 at 07:06:44PM +0300, Ivaylo Dimitrov wrote:
> On 1.09.23 г. 17:18 ч., Sean Young wrote:
> > The ir-rx51 is a pwm-based TX driver specific to the N900. This can be
> > handled entirely by the generic pwm-ir-tx driver, and in fact the
> > pwm-ir-tx driver has been compatible with ir-rx51 from the start.
> > 
> 
> Unfortunately, pwm-ir-tx does not work on n900. My investigation shows that
> for some reason usleep_range() sleeps for at least 300-400 us more than what
> interval it is requested to sleep. I played with cyclictest from rt-tests
> package and it gives similar results - increasing the priority helps, but I
> was not able to make it sleep for less that 300 us in average. I tried
> cpu_latency_qos_add_request() in pwm-ir-tx, but it made no difference.
> 
> I get similar results on motorola droid4 (OMAP4), albeit there average sleep
> is in 200-300 us range, which makes me believe that either OMAPs have issues
> with hrtimers or the config we use has some issue which leads to scheduler
> latency. Or, something else...

The pwm-ir-tx driver does suffer from this problem, but I was under the
impression that the ir-rx51 has the same problem.

> In either case help is appreciated to dig further trying to find the reason
> for such a big delay.

pwm-ir-tx uses usleep_range() and ir-rx51 uses hrtimers. I thought that
usleep_range() uses hrtimers; however if you're not seeing the same delay
on ir-rx51 then maybe it's time to switch pwm-ir-tx to hrtimers.

I don't have a n900 to test on, unfortunately.

Thanks
Sean

WARNING: multiple messages have this Message-ID (diff)
From: Sean Young <sean@mess.org>
To: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Cc: linux-media@vger.kernel.org, "Tony Lindgren" <tony@atomide.com>,
	"Russell King" <linux@armlinux.org.uk>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Timo Kokkonen" <timo.t.kokkonen@iki.fi>,
	"Pali Rohár" <pali.rohar@gmail.com>,
	"Sicelo A . Mhlongo" <absicsz@gmail.com>,
	linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org
Subject: Re: [PATCH v5 2/2] media: rc: remove ir-rx51 in favour of generic pwm-ir-tx
Date: Tue, 26 Sep 2023 08:16:33 +0100	[thread overview]
Message-ID: <ZRKFUb1vRtn82bgn@gofer.mess.org> (raw)
In-Reply-To: <99f0042f-538c-bcaf-96fd-bac24a87f88e@gmail.com>

On Mon, Sep 25, 2023 at 07:06:44PM +0300, Ivaylo Dimitrov wrote:
> On 1.09.23 г. 17:18 ч., Sean Young wrote:
> > The ir-rx51 is a pwm-based TX driver specific to the N900. This can be
> > handled entirely by the generic pwm-ir-tx driver, and in fact the
> > pwm-ir-tx driver has been compatible with ir-rx51 from the start.
> > 
> 
> Unfortunately, pwm-ir-tx does not work on n900. My investigation shows that
> for some reason usleep_range() sleeps for at least 300-400 us more than what
> interval it is requested to sleep. I played with cyclictest from rt-tests
> package and it gives similar results - increasing the priority helps, but I
> was not able to make it sleep for less that 300 us in average. I tried
> cpu_latency_qos_add_request() in pwm-ir-tx, but it made no difference.
> 
> I get similar results on motorola droid4 (OMAP4), albeit there average sleep
> is in 200-300 us range, which makes me believe that either OMAPs have issues
> with hrtimers or the config we use has some issue which leads to scheduler
> latency. Or, something else...

The pwm-ir-tx driver does suffer from this problem, but I was under the
impression that the ir-rx51 has the same problem.

> In either case help is appreciated to dig further trying to find the reason
> for such a big delay.

pwm-ir-tx uses usleep_range() and ir-rx51 uses hrtimers. I thought that
usleep_range() uses hrtimers; however if you're not seeing the same delay
on ir-rx51 then maybe it's time to switch pwm-ir-tx to hrtimers.

I don't have a n900 to test on, unfortunately.

Thanks
Sean

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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2023-09-26  7:16 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-01 14:18 [PATCH v5 0/2] Remove ir-rx51 driver Sean Young
2023-09-01 14:18 ` [PATCH v5 1/2] dt-bindings: media: remove nokia,n900-ir as pwm-ir-tx is compatible Sean Young
2023-09-02 10:50   ` Conor Dooley
2023-09-04 14:28     ` Lee Jones
2023-09-01 14:18 ` [PATCH v5 2/2] media: rc: remove ir-rx51 in favour of generic pwm-ir-tx Sean Young
2023-09-01 14:18   ` Sean Young
2023-09-06 16:04   ` Uwe Kleine-König
2023-09-06 16:04     ` Uwe Kleine-König
2023-09-25 16:06   ` Ivaylo Dimitrov
2023-09-25 16:06     ` Ivaylo Dimitrov
2023-09-26  7:16     ` Sean Young [this message]
2023-09-26  7:16       ` Sean Young
2023-09-26  7:37       ` Tony Lindgren
2023-09-26  7:37         ` Tony Lindgren
2023-09-26 12:54         ` Ivaylo Dimitrov
2023-09-26 12:54           ` Ivaylo Dimitrov
2023-09-26 12:43       ` Ivaylo Dimitrov
2023-09-26 12:43         ` Ivaylo Dimitrov
2023-09-26 20:18         ` Sean Young
2023-09-26 20:18           ` Sean Young
2023-09-29  8:49           ` Ivaylo Dimitrov
2023-09-29  8:49             ` Ivaylo Dimitrov
2023-09-29 16:20             ` Sean Young
2023-09-29 16:20               ` Sean Young
2023-09-29 21:08               ` Uwe Kleine-König
2023-09-29 21:08                 ` Uwe Kleine-König

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