linux-kernel - Re: [rfc]pwm: add xilinx pwm driver

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Message-ID: <20140515204941.GB7136@mithrandir>
Date:	Thu, 15 May 2014 22:49:42 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	monstr@...str.eu, Bart Tanghe <bart.tanghe@...masmore.be>,
	michal.simek@...inx.com, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, rob@...dley.net, grant.likely@...aro.org,
	linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [rfc]pwm: add xilinx pwm driver

On Thu, May 15, 2014 at 06:30:13PM +0200, Arnd Bergmann wrote:
> On Thursday 15 May 2014 15:56:03 Michal Simek wrote:
> > IP is configurable as is normal for us.
> > You can select IP with just one timer.
> > It means register locations for specific timer are fixed.
> > http://www.xilinx.com/support/documentation/ip_documentation/xps_timer.pdf
> > 
> > timer0 - offset 0x0
> > timer1 - offset 0x10 (doesn't need to be synthesized)
> > 
> > There is one interrupt for both timers.
> > 
> > Timers can be as timers (up/down count/ reload with or without IRQs)
> > But then one options is to use both timers and generate PWM signal.
> > From full ip description in DT you can see xlnx,gen0-assert = <1>;
> > which can suggest that this IP can output PMW signal.
> > (We can also detect if PWM0 signal is connected just to be sure
> > that PWM can be enabled).
> > 
> > There is also capture trigger mode where external signal start/stop
> > timer counting.
> > 
> > It means there are 3 modes - timer, capture and PWM.
> > Timer (clocksource, clockevent) requires specific handling,
> > PWM has own subsystem and not sure if there is any subsystem for
> > capture mode. Is there any?
> 
> I don't think so. Possibly somewhere in IIO.

I think so too. There was a patch set not so long ago that added PWM
capture support for one of the TI PWM controllers to IIO.

Thierry

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