linux-kernel - Re: [PATCH] [media] rc: ir-spi: add support for IR LEDs connected with SPI

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Date:	Fri, 01 Jul 2016 21:30:35 +0900
From:	Andi Shyti <andi.shyti@...sung.com>
To:	Sean Young <sean@...s.org>
Cc:	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	devicetree@...r.kernel.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, Andi Shyti <andi@...zian.org>
Subject: Re: [PATCH] [media] rc: ir-spi: add support for IR LEDs connected with
 SPI

Hi Sean,

> > The ir-spi is a simple device driver which supports the
> > connection between an IR LED and the MOSI line of an SPI device.
> > 
> > The driver, indeed, uses the SPI framework to stream the raw data
> > provided by userspace through a character device. The chardev is
> > handled by the LIRC framework and its functionality basically
> > provides:
> > 
> >  - raw write: data to be sent to the SPI and then streamed to the
> >    MOSI line;
> >  - set frequency: sets the frequency whith which the data should
> >    be sent;
> >  - set length: sets the data length. This information is
> >    optional, if the length is set, then userspace should send raw
> >    data only with that length; while if the length is set to '0',
> >    then the driver will figure out himself the length of the data
> >    based on the length of the data written on the character
> >    device.
> >    The latter is not recommended, though, as the driver, at
> >    any write, allocates and deallocates a buffer where the data
> >    from userspace are stored.
> > 
> > The driver provides three feedback commands:
> > 
> >  - get length: reads the length set and (as mentioned), if the
> >    length is '0' it will be calculated at any write
> >  - get frequency: the driver reports the frequency. If userpace
> >    doesn't set the frequency, the driver will use a default value
> >    of 38000Hz.
> 
> This interface is not compatible with other lirc devices; there is no
> way of determining whether this is a regular lirc device or this new
> flavour you've invented.

except of the set length and get length which I'm using a bit
freely because I am dealing with devices that exchange always the
same amount of data, so that I don't need (in my case) to
pre-allocate or overallocate or runtime allocate. I don't
understand what else I invented :)

This is a simple driver which is driving an LED connected through
SPI and userspace writes raw data in it (LIRC_CAN_SEND_RAW).

> Also I don't see what justifies this new interface. This can be 
> implemented in rc-core in less lines of code and it will be entirely 
> compatible with existing user-space.

Also here I'm getting a bit confused. When I started writing
this, I didn't even know of the existence of a remote controlling
framework, but then I run across this:

"LIRC is a package that allows you to decode and send infra-red
signals of many (but not all) commonly used remote controls. "

taken from lirc.org: my case is exactly falling into this
description.

Am I missing anything?

Thanks,
Andi