How to define an I2C-to-SPI bridge device ?

Grant Likely grant.likely at
Sat Sep 11 04:28:15 EST 2010

On Fri, Sep 10, 2010 at 08:14:44PM +0200, André Schwarz wrote:
> > > At first I thought about registering 4 SPI busses representing the 4 cs#
> > > lines and hide the cs# generation from the user. This would make
> > > multiple cs# assertions for a single write impossible which is a very
> > > useful feature.
> > 
> > The SPI subsystem doesn't directly support this use-case.  If you want
> > to do this, then assign another chip select number for the purpose of
> > enabling multiple CS lines at once... and be careful which drivers you
> > allow to be bound to the oddball CS number.  The in-kernel drivers
> > certainly don't support this use-case, and care must be taken to
> > ensure only one device is writing to the input line at a time.
> > 
> > What specific hardware do you need this feature for?
> We have a board with multiple parallel video transmitters connected to
> an FPGA. Video timing and general parameters are always the same and
> there are quite a lot of settings to write during init/mode change.
> Doing this in parallel will speed things up significantly.

Yeah; Then I would handle it as a separate cs# and map it to enabling
multiple CS lines at a time.

> BTW: would "drivers/misc" be a proper location ?
> Who's supposed to pick that driver up and on what list shall I post it
> for review ?

You should cc spi-devel-general, and feel free to cc me.  drivers/misc
would probably be an okay place for it to live; but if it only appears
on a single machine, then it may make more sense in
arch/*/<board-directory>.  What arch or SoC is this running on?


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