Message-ID: <564780F6.5040300@kernel.org>
Date:	Sat, 14 Nov 2015 18:44:06 +0000
From:	Jonathan Cameron <jic23@...nel.org>
To:	Marc Titinger <mtitinger@...libre.com>,
	Lars-Peter Clausen <lars@...afoo.de>, knaack.h@....de,
	pmeerw@...erw.net
Cc:	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	mturquette@...libre.com, bcousson@...libre.com,
	ptitiano@...libre.com
Subject: Re: [RFC 4/4] iio: ina2xx: add SOFTWARE buffer mode using an iio
 kfifo.

On 12/11/15 10:18, Marc Titinger wrote:
> On 10/11/2015 19:23, Lars-Peter Clausen wrote:
>> On 11/10/2015 05:07 PM, Marc Titinger wrote:
>>> Capture the active scan_elements into a kfifo.
>>> The capture thread will compute the remaining time until the next capture
>>> tick, and do an active wait (udelay).
>>>
>>> This will produce a stream of up to fours channels plus a 64bits
>>> timestamps (ns).
>>>
>>> # iio_readdev ina226 |  od -x
>>> WARNING: High-speed mode not enabled
>>> 0000000 042f 0d5a 002e 010c 4be8 4eb4 0013 0000
>>> 0000020 0430 0d5a 002e 010c a704 4f3e 0013 0000
>>> 0000040 0430 0d5a 002e 010c b477 4fc7 0013 0000
>>> 0000060 042f 0d5b 002e 010c 8052 5050 0013 0000
>>> 0000100 042f 0d5b 002e 010c 5d92 50d8 0013 0000
>>> 0000120 0430 0d5a 002e 010c fa59 515e 0013 0000
>>> 0000140 0430 0d5b 002e 010c 95d2 51e5 0013 0000
>>>
>>> Signed-off-by: Marc Titinger <mtitinger@...libre.com>
> 
> Hi Lars,
> 
>>
>> Interesting approach. I think if we are going to due this we want to make
>> this kind of emulation generic. Have you seen the software trigger and
>> configfs support patches[1] from Daniel? It kind of achieves the same as you
>> do, but using hrtimers.
> 

> I totally agree, let me have a look on those patches maybe I could
> add an active waiting scheme for platforms w/o hrtimers ?
I've no idea if this is a remotely common case any more but in theory
I'd have no objection to such a patch though I would like it to be
a stand alone trigger similar to that used in the patch Daniel has
submitted.

>>
>>>
>>> ---
>>> Ina2xx does not support auto-increment, hence the capture threads sticks
>>> with single register reads instead of regmap_bulk_read.
>>>
>>> The proper scales must be applied to those raw register
>>> values, I'm in favor of doing the conversion in userland in a client plugin
>>
>> Yes, conversion should not be done in kernel space, we don't want to impose
>> the performance penalty on users which don't need it and you can typically
>> do it faster in userspace anyway where you have floats and SSE and what not.
>>
>>> for instance a sigrok
>>
>> Slightly OT, but do you already have some Sigrok IIO support? I have this
>> scheduled for end of the month, maybe we can align our strategies here and
>> avoid duplicated work.
> 

> How fortunate! I've started some preliminary work like cloning the
> demo driver into a skeletton for 'hardware/generic-iio/api.c', adding
> the build/ac plumbing, and linking to libiio with the idea of using
> iio_info to create a generic enumeration of the iio-context into
> sigrok channels.
> 
> Now, I'm not familiar with Glib and it might not be my prio until a
> couple of weeks, so I'd be super happy to wait for you if you are
> keen to do that part :)
> 
> What would be the best spot to chat about this ?
> 

> Marc.
> 
> 
>>
>> - Lars
>>
>> [1] https://lkml.org/lkml/2015/8/10/877
>>
> 
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