Look in the kernel source....  drivers/gpio/Kconfig
 
MAX7300
MAX732X
PCA953X
PCF857X
ADP5588
 
So looks like you have to write a new driver for that Microchip part.


From: coderdrone@gmail.com [mailto:coderdrone@gmail.com]
Sent: Wednesday, March 24, 2010 10:03 AM
To: General mailing list for gumstix users.
Subject: Re: [Gumstix-users] I2C

How do I determine if the chip is supported by kernel drivers?  I'm told we'll be using the MCP23017.  This is on Gumstix Overo.

The pins we were told to use on the expansion board are GPA# instead of GPIO### (e.g., GPA0 vs. GPIO171).  If these are exposed in /sys/class/gpio/GPA# similarly to GPIOs, that would be great.

On Mon, Mar 22, 2010 at 9:22 AM, Matt Singer <msinger@eastcoreng.com> wrote:
 
Yes, if you use one of the chips that are supported by kernel drivers.
 
 

From: coderdrone@gmail.com [mailto:coderdrone@gmail.com]
Sent: Monday, March 22, 2010 9:15 AM

To: General mailing list for gumstix users.
Subject: Re: [Gumstix-users] I2C

I've recently been informed that our project will be using IO expansion boards on the i2c bus for our project.  Do the GPIO pins on these boards get exposed in sysfs in the same way as the pins coming off the 40-pin header of the summit board?  With the pins on the header, they all show up in /sys/class/gpio and I can read/write to them as normal files.

With the i2c-connected expansion cards, will I be able to do this as well?  e.g., echo XXX > /sys/class/gpio/export && echo 0 > /sys/class/gpio/gpioXXX/value.

On Mon, Mar 22, 2010 at 7:25 AM, Matt Singer <msinger@eastcoreng.com> wrote:

Thanks for the explanation Dave.  Still seems odd as the address that
Honeywell states is a +1 for read so it would be that the low order bit is
R/W. And that addressing is how I've used it with PICS and with RS232->I2C
chips.

Regardless, I just hope the info spares others some time and frustration.


-----Original Message-----
From: Dave Hylands [mailto:dhylands@gmail.com]
Sent: Saturday, March 20, 2010 12:12 PM
To: General mailing list for gumstix users.
Subject: Re: [Gumstix-users] I2C

Hi,

On Sat, Mar 20, 2010 at 7:51 AM,  <msinger@eastcoreng.com> wrote:
> One thing I found when using reading/writing to i2c-3 is that the
> driver shifts the address you give it in the ioctl left by 1.  Maybe
> that's a documented feature, but it caused me a lot of pain.

That's because the address is a 7-bit field and occupies the upper 7-bits of
the first byte. The bottom bit is a R/W bit. Lots of vendors mash the two
things together and call it the address byte, which is where the confusion
comes from.

They'll further confuse things by saying  that there is a read address and a
write address, when,in fact, there is a single address with a R/W bit.

The authors of the linux driver decided to use the terminology found in the
i2c specification.

--
Dave Hylands
Shuswap, BC, Canada
http://www.DaveHylands.com/

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