[i2c] [RFC PATCH 3/8] Philips PCA9536 4 bit I2C GPIO extender driver

[David Brownell]

On Sunday 27 January 2008, Jean Delvare wrote:
> 
> There is a new GPIO subsystem (under driver/gpio), that's where you
> should add this driver.

That should merge soonish into kernel GIT -- Linus is merging up a
storm before LCA starts, but Andrew's not sent it yet -- but it's
easy to grab from current MM.

There's a pca9539 driver there, and ISTR the 9536 is very similar
except it has no IRQ support and only has 8-bit registers.  You
should be able to reuse its platform_data structure.  It has a
registration callback that should let you establish the linkage to
the camera(s) you want to control.

I suspect you'll come across one other issue... one potential fix
being to add a mechanism matching a NOTE in the gpiolib sources.

I think you should consider making one driver that can handle three
chips: the 4-bit pca9536 (8 pins) and pca9537 (10 pins -- add irq and
reset), plus their 8-bit pca9538 sibling (16 pins -- four more GPIOs,
and two address bits).  Their register model is *identical* ... all
that would mean is understanding that for some chips the high nibble
is actually valid.  (And eventually, maybe, that some chips support
input-changed IRQs that can help avoid synchronous register reads.
If the i2c_client doesn't list an IRQ that's of course not an issue.)

- Dave