Re: [PATCH] Add support for slave controllers plus sysfs entries for power management

From: jassi brar <jassisinghbrar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: Linus Walleij <linus.ml.walleij-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: spi mailing list
	<spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>,
	Ken Mills <ken.k.mills-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Subject: Re: [PATCH] Add support for slave controllers plus sysfs entries for power management
Date: Wed, 17 Feb 2010 10:43:12 +0900	[thread overview]
Message-ID: <1b68c6791002161743w52da3a4h128b59c42e0602dc@mail.gmail.com> (raw)
In-Reply-To: <63386a3d1002161133k501e51f4xf4e94a307cb4fcf5-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>

On Wed, Feb 17, 2010 at 4:33 AM, Linus Walleij
<linus.ml.walleij-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> 2010/2/15 jassi brar <jassisinghbrar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>:
>
>> I don't think adding SPI_SLAVE support is just a matter of providing
>> additional callbacks and structures, as is pointed out in this thread....
>> http://www.mail-archive.com/spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org/msg00368.html
>
> You mean that the responsiveness / control of latencies is the other thing
> that's needed? Yep so it is. But getting the infrastructure in place doesn't
> hurt because this is something many people (including self) need and Ken
> over at Intel is the only one actually doing something about it.
>
> Getting SPI slaves to actually work by spawning their worker threads as
> realtime under that patchset is of course a larger issue. One does not
> exclude the other tho.
I tend to resonate with Ned Forrester's concerns and Grant Likely
already has clarified my point.

As a further note, it *seems* someone just needs a way to test his SPI
controller's SLAVE mode(I used to do that with much lesser changes
to the SPI stack). Or I will be interested to know (to the extent
your privilege to disclose extends) which device running a full fledged
non-real time OS(Linux) needs to work as a SPI slave?
I have been supporting Samsung's SPI drivers internally for quite
some time now and am yet to come across one usage of it's SLAVE
mode. Also, it's only intuitive that 'chips'(with minimal f/w, fixed
functionality and bounded delays) run as SPI SLAVE and
devices(with multiple processes and indeterminate latencies) as
MASTER.

So, I am not excited about (*coughs*) seeing SPI SLAVE support
implemented without (a) real need for it (b) properly thought out
architecture and not just a workaround.

regards.

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