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

[Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>]

On Sun, Feb 14, 2010 at 6:37 PM, jassi brar <jassisinghbrar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> On Mon, Feb 15, 2010 at 8:20 AM, Linus Walleij
> <linus.ml.walleij-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> 2010/1/19 Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>:
>>
>>>  The current model is that each spi_device is registered with an
>>> spi_master.  Many device drivers operate on the assumption that the
>>> ->master pointer is valid.  With this patch, it appears that
>>> spi_devices can be registered either against an spi_master or an
>>> spi_slave; thus invalidating the assumption drivers are already
>>> operating under.  That alone makes me nervous.
>>
>> IIRC in my last review of this patch I proposed that drivers be
>> either master, slave or both. With the current approach that would
>> mean putting  #ifdefs over the ->master as well and making master
>> support optional. (You can even #ifdef out these parts of the struct
>> to be absolutely sure.)
>
> 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
>
> We'd better see if the implementation covers at least some aspects of
> being a SPI slave,
> otherwise it seems more like a 'workaround' than support.

I agree.  I need to see a real usage model before I merge anything.
As it stands right now, spi_master looks like an entirely different
thing from an spi_slave, even if both happen to use spi_messages
(although spi_message only seems to handle a small number of the
possible spi slave use cases.  For example, it doesn't address at all
a command and response within the same SPI transfer).  I don't at all
like the idea of allowing the current spi_device to be registered on
either an spi_master or an spi_slave.

I may let a driver through that happens to turn on an SPI slave mode
in the hardware, but if you're doing that, be aware that it may be an
abuse of the spi_master model, and you'll get little sympathy when
breakage happens.

I haven't seen anything spi_slave related yet that I'll merge in the
common spi code.

g.

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