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

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Message-ID: <5375CFEC.6070008@monstr.eu>
Date:	Fri, 16 May 2014 10:44:28 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Thierry Reding <thierry.reding@...il.com>,
	Arnd Bergmann <arnd@...db.de>
CC:	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,
	Matt Porter <matt.porter@...aro.org>
Subject: Re: [rfc]pwm: add xilinx pwm driver

On 05/15/2014 10:49 PM, Thierry Reding wrote:
> 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.

It is probably this.
https://lwn.net/Articles/583998/
https://lkml.org/lkml/2014/2/5/378

There were some comments in v3 which haven't been fixed.
Matt: What's the status on this?

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform



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