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

On Tue, Feb 16, 2010 at 12:33 PM, Linus Walleij
[off-list ref] wrote:

2010/2/15 jassi brar [off-list ref]:

quoted

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.

No, the model needs to be in place first.  That means describing the
model for spi_slave transfers.  Does the driver need to turn around
and respond mid-transfer?  Does there need to be latency controls?
How are protocol drivers interfaced with spi slave controllers (1 to
1, or 1 to many, how is the protocol selected)?

I appreciate the work Ken is doing, but the patches posted so far
abuse the spi_master model in a way I'm not willing to merge.  I think
spi_slave is a different enough thing that it warrants an entirely
different core infrastructure (but I do reserve the right to have my
mind changed).

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.

Your right, the realtime issues are separate, but I still need to see
how spi_slave devices are intended to work, and what the
strengths/limitations of the model are.

g.

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