Hi Benjamin,
On January 7th, 2006, Benjamin Herrenschmidt asked:
> Can you confirm the difference between writing a block of data with
> I2C_SMBUS_BLOCK_DATA vs I2C_SMBUS_I2C_BLOCK_DATA on the wire ? It's my
> understanding that the former will actually send the length byte on the
> wire before the data while the later won't, though they both send a
> subaddress.
I confirm you are correct.
> I'm completely rewriting the powermac i2c support (consolidating all
> busses behind a low level layer that I need to use in circumstances
> where the linux i2c layer isn't useable, and with a single driver in
> drivers/i2c/busses/* replacing i2c-keywest.c and i2c-pmac-smu.c) and I
> think I'm hitting a problem where i2c-keywest didn't implement
> I2C_SMBUS_BLOCK_DATA properly (didn't send the length byte) and some
> drivers (our sound drivers) rely on that behaviour (that's fine, I can
> fix them too, I just want to make sure I understand what the semantic
> should be).
I just took a quick look at i2c-keywest.c and you seem to right: the
driver supposedly implements SMBus block transfers
(I2C_SMBUS_BLOCK_DATA) but the actual implementation pretty much looks
like I2C block transfers (I2C_SMBUS_I2C_BLOCK_DATA). Good catch.
> I'm a bit surprised that there seem to be no wrapper for writing with
> I2C_SMBUS_I2C_BLOCK_DATA, only for reading, in i2c-core.c since it
> appears to me that it's the most common one, at least for all devices
> I've dealt with so far (mostly sound & clock chips in addition to
> sensors)...
I suspect that these drivers which do I2C block writes do so by calling
i2c_master_send (or even i2c_transfer) directly, rather than relying on
the SMBus compatibility layer.
The i2c_smbus_write_i2c_block_data wrapper function used to be defined,
but was removed in 2.6.10-rc2 together with a couple other similar
wrappers [1] on request by Adrian Bunk, the reason being that they had
no user back then. I was a bit reluctant at first, but we finally agreed
with Adrian to remove the functions, and to reintroduce them later if
they were ever needed.
So, if you need i2c_smbus_write_i2c_block_data(), we can easily
resurrect it. See the patch below. I made the new version a bit faster
(I hope) than the original by using memcpy, please confirm it works for
you.
[1] http://jdelvare.net2.nerim.net/quian/2.6-wrc/diff.php?patch=patch-2.6.10-rc1-rc2.bz2&file=include/linux/i2c.h
http://jdelvare.net2.nerim.net/quian/2.6-wrc/diff.php?patch=patch-2.6.10-rc1-rc2.bz2&file=drivers/i2c/i2c-core.c
* * * * *
Resurrect i2c_smbus_write_i2c_block_data.
Signed-off-by: Jean Delvare <[email protected]>
---
drivers/i2c/i2c-core.c | 15 +++++++++++++++
include/linux/i2c.h | 3 +++
2 files changed, 18 insertions(+)
--- linux-2.6.15-git.orig/drivers/i2c/i2c-core.c 2006-01-08 10:55:58.000000000 +0100
+++ linux-2.6.15-git/drivers/i2c/i2c-core.c 2006-01-08 11:17:57.000000000 +0100
@@ -948,6 +948,20 @@
}
}
+s32 i2c_smbus_write_i2c_block_data(struct i2c_client *client, u8 command,
+ u8 length, u8 *values)
+{
+ union i2c_smbus_data data;
+
+ if (length > I2C_SMBUS_BLOCK_MAX)
+ length = I2C_SMBUS_BLOCK_MAX;
+ data.block[0] = length;
+ memcpy(data.block + 1, values, length);
+ return i2c_smbus_xfer(client->adapter, client->addr, client->flags,
+ I2C_SMBUS_WRITE, command,
+ I2C_SMBUS_I2C_BLOCK_DATA, &data);
+}
+
/* Simulate a SMBus command using the i2c protocol
No checking of parameters is done! */
static s32 i2c_smbus_xfer_emulated(struct i2c_adapter * adapter, u16 addr,
@@ -1152,6 +1166,7 @@
EXPORT_SYMBOL(i2c_smbus_write_word_data);
EXPORT_SYMBOL(i2c_smbus_write_block_data);
EXPORT_SYMBOL(i2c_smbus_read_i2c_block_data);
+EXPORT_SYMBOL(i2c_smbus_write_i2c_block_data);
MODULE_AUTHOR("Simon G. Vogl <[email protected]>");
MODULE_DESCRIPTION("I2C-Bus main module");
--- linux-2.6.15-git.orig/include/linux/i2c.h 2006-01-08 10:56:08.000000000 +0100
+++ linux-2.6.15-git/include/linux/i2c.h 2006-01-08 11:02:00.000000000 +0100
@@ -100,6 +100,9 @@
/* Returns the number of read bytes */
extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
u8 command, u8 *values);
+extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
+ u8 command, u8 length,
+ u8 *values);
/*
* A driver is capable of handling one or more physical devices present on
--
Jean Delvare
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
