linux-kernel - Re: [PATCH] PWM: atmel: fix incorrect CDTY value after enabling or disabling

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Message-ID: <20140825115454.GA2077@piout.net>
Date:	Mon, 25 Aug 2014 13:54:54 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Bo Shen <voice.shen@...el.com>, linux-pwm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] PWM: atmel: fix incorrect CDTY value after enabling or
 disabling

Hi,

On 25/08/2014 at 12:15:23 +0200, Thierry Reding wrote :
> On Fri, Mar 14, 2014 at 08:05:31PM +0100, Alexandre Belloni wrote:
> > pwm-leds calls .config() and .disable() in a row. This exhibits that it may
> > happen that the channel gets disabled before CDTY has been updated with CUPD.
> > The issue gets quite worse with long periods.
> > So, ensure by reading ISR that at least one period has past before disabling the
> > channel.
> > 
> > The other issue is that it may happen that CUPD is not flushed before enabling
> > the channel so it will update CDTY/CPRD just after one period. So we always set
> > CUPD, even when the channel is not enabled.
> > 
> > Tested on at91sam9g45 and sama5d31ek.
> > 
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> > ---
> >  drivers/pwm/pwm-atmel.c | 46 +++++++++++++++++++++++++++++-----------------
> >  1 file changed, 29 insertions(+), 17 deletions(-)
> 
> going through the list of unapplied patches I came across this old
> patch. It was never reviewed nor acked by anyone and you didn't ping me,
> so I always assumed it must no longer be required. Is that so?
> 

It is still required but Nicolas is not happy with the polling on
PWM_ISR and he was supposed to discuss that internally with the IP
designer to understand if there is a better way.

I'll either ping on that one or send a new version when I'll know a bit
more.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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