On Fri, May 27, 2011 at 12:33:18PM +0200, Thomas De Schampheleire wrote:

On Fri, May 27, 2011 at 9:17 AM, Grant Likely [off-list ref] wrote:

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On Wed, May 25, 2011 at 08:39:26AM +0200, Thomas De Schampheleire wrote:

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Hi,

On Mon, May 23, 2011 at 10:13 AM, Thomas De Schampheleire
[off-list ref] wrote:

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Hi Grant,

On Thu, May 19, 2011 at 5:58 PM, Grant Likely [off-list ref] wrote:

quoted

On Thu, May 19, 2011 at 05:32:32PM +0200, Thomas De Schampheleire wrote:

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Hi,

I am using the uio framework (userspace i/o) to handle devices in
userspace. This includes memory access and interrupt handling.
For i2c devices, I'm using the i2c-dev interface, to talk to these
devices from userspace. This already works fine.

One of my i2c devices also has an interrupt line connected to the
processor. To be able to handle this interrupt with uio, I need to
have a kernel driver matched against the i2c device. However, the i2c
device described in the device tree does not bind with the driver. Is
this behavior supported, and if so, what am I doing wrong? Do I have
to create a dummy bus (non-i2c) and add a shadow node for the
interrupt?

You're wandering into new territory here.  It is definitely the right
thing to do to describe your i2c device in the device tree with the
interrupt fully specified.

What you probably need to do is create a uio helper driver for your
device that takes care of finding the device node, mapping the
interrupt, and proving the interrupt handling UIO hook to userspace.
The easiest way to work this out would be to make your uio helper
actually bind to the i2c device created by the device node (this is
probably the best way too), but you don't have to.  As long as you
arrange for you uio helper to get called at some point, you can get it
to find the appropriate node in the DT, map the interrupt, and export
it to userspace.

Binding the helper driver with the i2c device in the device tree is
indeed what I am trying to achieve. Unfortunately, the binding does
not happen, the probe function of my driver never gets called.

For the other UIO devices in this system (non-I2C), the mechanism is as follows:
1. the devices are described in the device tree, as children under
their respective bus node (e.g. localbus)
2. the platform code (arch/powerpc/platforms/85xx/corenet_ds.c)
iterates over all buses it understands, among which 'simple-bus'.
3. for each child device on the bus, a bind operation with a driver is
attempted, based on the device 'compatible' string

This works perfectly.
However, the i2c bus does not have any of the matched bus types, like
simple-bus, and as such it is handled differently. The i2c bus driver
(drivers/i2c/busses/i2c-mpc.c) calls of_register_i2c_devices (in
drivers/of/of_i2c.c), which handles the i2c-specific part of the
device, but does not (as far as I understand and observe) treat the
device as a regular device with a match table.

Maybe I misunderstand something. Is this where I need to play with
modaliases? How does this work in the context of device trees?

quoted

g.

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My device tree nodes look like this:

        soc@fe000000 {
                i2c@118100 {
                        #address-cells = <1>;
                        #size-cells = <0>;
                        cell-index = <1>;
                        compatible = "fsl-i2c";
                        reg = <0x118100 0x100>;
                        interrupts = <38 2 0 0>;
                        dfsrr;
                        mydevice@68 {
                                compatible = "mymanufacturer,mydevice";
                                reg = <0x68>;
                                interrupts = <7 1 0 0>; /* External
IRQ7, active-low level */
                        };
                };

This looks to be correct.

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The device driver then has:

static const struct of_device_id mydevice_ids[] = {
        {
                .compatible = "mymanufacturer,mydevice"
        },
        {},
};
static struct of_platform_driver mydevice_driver = {

You don't want to do this.  This is an i2c device, not a platform
device.  If anything, this should be an i2c_driver and you should use
the normal creation of i2c devices from the DT.

Ok, so this may be the reason why my driver does not get registered
against the device...

I have it working now. The bottom line was indeed, as you hinted, to
transform the platform driver into an i2c driver, and make sure that
it gets bound to the device. Here indeed, I need to specify the right
modalias in the compatible string.

Glad to hear.  Thanks for reporting back.  Comments below.

Seems that I spoke too soon.
Although the binding of the device and the driver works correctly, I
now have problems with using the i2c device from userspace. After
having transformed my platform driver into an i2c driver, setting the
same slave address from userspace fails. This is not what I wanted.

How do I get around this? To get proper binding I need an I2C device,
but to be able to use i2c-dev I shouldn't have an I2C device.

You're venturing into new territory here.  You'll either need to adapt
i2c-dev to coexist peacefully with a real i2c_client device, or you'll
need to modify i2c-dev to parse the device tree and decode the irq for
you.

It seems that Arnd's suggestion to make i2c-dev interrupt aware, comes
into play here. However, how will i2c-dev know which interrupts belong
to which device? To use i2c-dev without interrupts, all you need in
the device tree is the i2c controller nodes.

You'll need i2c-dev to find the associated node in the device tree,
possibly with an ioctl call.  I don't know the best way to proceed
here, sorry.  Jean might have better suggestions, but in general I
don't think i2c-dev is intended to provide any irq infrastructure.

g.