Re: pca953x GPIO

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

Hi Giampaolo,

On Wed, 23 Jun 2010 14:02:04 +0200, Giampaolo Bellini wrote:
> Hi all...
> 
>   I'm new to I2c and I'm in trouble trying to get GPIO works on an
> Advantech PCM-3362 motherboard.
> 
> manufacturer says that GPIO controller is an NXP PCA9555PW chip,
> attached to the i2c BUS; the chip has the addresses 40 (read) and 41
> (write) but, if I'm not wrong, in his linux libsusi library

This means they refer to left-aligned addresses. Linux uses
right-aligned addresses, so your device lives at 0x20 as far as Linux
is concerned.

> manufacturer access GPIO via BIOS calls and not via linux i2c.
> 
> CPU is an intel Atom N450 with ICH8M chipset and it seems that SMBUS
> controller is correctly recognized by the kernel as dmegs reports
> something like:
> i801_smbus 0000:00:1f.3: PCI INT C -> GSI 17 (level, low) -> IRQ 17
> 
> actually I've configured the latest 2.6.34 kernel with i2c and pca953x
> drivers, but /sys/class/gpio reports only import / export entries,
> with no GPIO chips at all...
> 
> I've read Documents/gpio.txt but still don't understand if I have to
> do something more to enable GPIO: as I want to access it from kernel
> space, I think I'll need to write my own driver (calling
> gpio_request() etc) but still miss info about GPIO numbers... and I'm
> not even sure GPIO is currently detected.

Check arch/arm/mach-ks8695/board-acs5k.c and
arch/arm/mach-pxa/cm-x300.c for examples.

> Ive try also registering a new GPIO device using generic gpiolib &
> sysfs support (eg: echo GPIO-RD 0x40 >
> /sys/bus/i2c/devices/i2c-0/new_device) but with no success.

Wrong name and wrong address, no surprise it didn't work. Try instead:

echo pca9555 0x20 > /sys/bus/i2c/devices/i2c-0/new_device

(Assuming i2c-0 is the bus on which the chip actually lives - you can
check with i2cdetect). That being said, I doubt that a GPIO chip can
really be instantiated from user-space, as it needs configuration
settings which you can't provide that way.

-- 
Jean Delvare
http://khali.linux-fr.org/wishlist.html