Adding GPIO/SPI/I2C functionality to FTDI driver

[chrysn]

Hallo Stefan, hallo Philipp,
hello Johan and Greg,

On Tue, Sep 22, 2015 at 12:02:03PM -0700, Greg KH wrote:
> On Tue, Sep 22, 2015 at 06:28:47PM +0200, chrysn wrote:
> > Is support for alternative operation modes in FTDI chips something that
> > is welcome and (easily) feasible in the kernel?
> 
> This comes up every other month or so on the linux-usb mailing list.
> See the discussions there about how to do this properly in a way that
> will be accepted by the USB maintainers if you wish to do this work.

I've overlooked your two recent approaches when looking for existing
approaches towards extending FTDI support in the kernel (probably due to
me being too focused at SPI).

Stefan and Philipp, has any of your patch sets received updates in the
meantime that have not been sent to the mailing list?

It seems that one issue that needs to be solved for either of those to
continue is the decision of whether to base the FTDI driver on the MFD
infrastructure (which would probably be a first step then before even
implementing any of SPI, GPIO or I2C interfaces). There have been
conflicting opinions on this in different threads ([1], [2]); my
impression is that it would be a good idea, given that many of the more
recent FTDI devices can be switched to half a dozen configurations, and
that they are also shipped in products[3] where several of them would be
used in a coordinated fashion similar to the shields of widespread
embedded systems.

Johan and Greg, can you reconcile your opinions on that? Or whom is that
question best discussed with? devicetree? linux-usb?  linux-gpio / -spi
/ -i2c?

Best regards
chrysn

PS. I've updated the summary I'm keeping of what led to this thread on
[4] -- all directly relevant information / questions should be in the
mails, but the page should provide further background for the curious.

[1] https://lkml.org/lkml/2014/6/1/250
[2] https://lkml.org/lkml/2015/6/22/451
[3] http://www.mikroe.com/click/usb-adapter/
[4] http://christian.amsuess.com/idea-incubator/ftdi-kernel-support/

-- 
I shouldn't have written all those tank programs.
  -- Kevin Flynn
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