linux-kernel - Re: [RFC 4/4] iio: ina2xx: add SOFTWARE buffer mode using an iio kfifo.

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Date:	Thu, 12 Nov 2015 11:18:02 +0100
From:	Marc Titinger <mtitinger@...libre.com>
To:	Lars-Peter Clausen <lars@...afoo.de>, jic23@...nel.org,
	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 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 ?

>
>>
>> ---
>> 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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