I2C node in device tree breaks old-style drivers

I2C node in device tree breaks old-style drivers

[Timur Tabi]

I'm trying to debug an I2C problem I've found in my old-style driver:
sound/soc/codecs/cs4270.c.  My I2C probe function is working, but the I2C
subsystem cannot find my device.  I know it's there, because U-Boot can probe it
just fine.

At first, I thought my problem was this:

static struct i2c_driver cs4270_i2c_driver = {
	.driver = {
		.name = "CS4270 I2C",
		.owner = THIS_MODULE,
	},
	.id =             I2C_DRIVERID_CS4270,
	.attach_adapter = cs4270_i2c_attach,
	.detach_client =  cs4270_i2c_detach,
};

In a slightly older kernel (still 2.6.27), I had to change "CS4270 I2C" to
"cs4270" to get it to work.  However, that change no longer makes a difference.

I turned on debugging and this is what I see:

i2c-core: driver [CS4270 I2C] registered
i2c-adapter i2c-0: found normal entry for adapter 0, addr 0x48
i2c-adapter i2c-0: master_xfer[0] W, addr=0x48, len=0
i2c-adapter i2c-0: found normal entry for adapter 0, addr 0x49
i2c-adapter i2c-0: master_xfer[0] W, addr=0x49, len=0
i2c-adapter i2c-0: found normal entry for adapter 0, addr 0x4a
i2c-adapter i2c-0: master_xfer[0] W, addr=0x4a, len=0
i2c-adapter i2c-0: found normal entry for adapter 0, addr 0x4b
i2c-adapter i2c-0: master_xfer[0] W, addr=0x4b, len=0
i2c-adapter i2c-0: found normal entry for adapter 0, addr 0x4c
i2c-adapter i2c-0: master_xfer[0] W, addr=0x4c, len=0
i2c-adapter i2c-0: master_xfer[0] W, addr=0x4c, len=1
i2c-adapter i2c-0: master_xfer[1] R, addr=0x4c, len=1
i2c-adapter i2c-0: found normal entry for adapter 0, addr 0x4d
i2c-adapter i2c-0: master_xfer[0] W, addr=0x4d, len=0
i2c-adapter i2c-0: master_xfer[0] W, addr=0x4d, len=1
i2c-adapter i2c-0: master_xfer[1] R, addr=0x4d, len=1
i2c-adapter i2c-0: found normal entry for adapter 0, addr 0x4e
i2c-adapter i2c-0: master_xfer[0] W, addr=0x4e, len=0
i2c-adapter i2c-0: found normal entry for adapter 0, addr 0x4f

My device is at address 4F.  The device tree defines a node for this device.
You can see it in arch/powerpc/boot/dts/mpc8610_hpcd.dts.

When I change the device tree so that it lists the device at an address other
than 4F, (e.g. "reg = <0x48>"), then my driver works.

So my conclusion is that specifying an I2C node in the device tree *requires*
that the driver be new-style.  Is there any way we can fix this?  I'm not going
to have time to update the CS4270 driver to a new-style interface before the
2.6.27 window closes.

-- 
Timur Tabi
Linux kernel developer at Freescale

Re: I2C node in device tree breaks old-style drivers

[Jochen Friedrich]

Hi Timur,

> So my conclusion is that specifying an I2C node in the device tree *requires*
> that the driver be new-style.  Is there any way we can fix this?  I'm not going
> to have time to update the CS4270 driver to a new-style interface before the
> 2.6.27 window closes.

This conclusion is correct. One possible way to fix this is to add support for
blacklisting to drivers/of/base.c (untested):

[RFC] of: Support blacklisting and blacklist cs4270.

Signed-off-by: Jochen Friedrich <jochen@scram.de>
---
 drivers/of/base.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index ad8ac1a..8c53b2c 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -404,13 +404,16 @@ EXPORT_SYMBOL(of_find_matching_node);
  * assumed that the data size is small and that the compatible values
  * should already be distinct enough to differentiate between SPI, I2C
  * and other devices.
+ *
+ * Blacklisting devices is supported by using NULL as modalias.
  */
 struct of_modalias_table {
 	char *of_device;
 	char *modalias;
 };
 static struct of_modalias_table of_modalias_table[] = {
-	/* Empty for now; add entries as needed */
+	/* Blacklisting cs4270 as this driver is currently old-style. */
+	{ "cirrus,cs4270",	NULL }
 };

 /**
@@ -441,6 +444,9 @@ int of_modalias_node(struct device_node *node, char *modalias, int len)
 		compatible = of_modalias_table[i].of_device;
 		if (!of_device_is_compatible(node, compatible))
 			continue;
+		/* Check for blacklisting */
+		if (!of_modalias_table[i].modalias)
+			return -ENODEV;
 		strlcpy(modalias, of_modalias_table[i].modalias, len);
 		return 0;
 	}
-- 
1.5.6.3

Re: I2C node in device tree breaks old-style drivers

[Timur Tabi]

On Wed, Jul 30, 2008 at 5:54 AM, Jochen Friedrich <jochen@scram.de> wrote:
> Hi Timur,
>
>> So my conclusion is that specifying an I2C node in the device tree *requires*
>> that the driver be new-style.  Is there any way we can fix this?  I'm not going
>> to have time to update the CS4270 driver to a new-style interface before the
>> 2.6.27 window closes.
>
> This conclusion is correct. One possible way to fix this is to add support for
> blacklisting to drivers/of/base.c (untested):

No need.  I posted a patch to alsa-devel that makes the CS4270 a
new-style I2C driver.  I'd hate to think that my driver is the only
I2C driver used on PowerPC systems that was outdated. :-)


-- 
Timur Tabi
Linux kernel developer at Freescale