Re: [PATCH] i2c: Split I2C_M_NOSTART support out of I2C_FUNC_PROTOCOL_MANGLING
From: Jean Delvare <hidden>
Date: 2012-05-03 18:36:17
Also in:
linux-i2c, linux-input
Hi Mark, On Thu, 3 May 2012 11:53:36 +0100, Mark Brown wrote:
Since there are uses for I2C_M_NOSTART which are much more sensible and standard than most of the protocol mangling functionality (the main one being gather writes to devices where something like a register address needs to be inserted before a block of data) create a new I2C_FUNC_NOSTART for this feature and update all the users to use it.
This is all correct, but it should be documented in Documentation/i2c/i2c-protocol. At the moment documentation still says that I2C_M_NOSTART is a weird protocol quirk nobody should be using. When you update the documentation, I think it is important to stress that there are now two use cases of I2C_M_NOSTART. If direction changes, it is a rarely needed protocol quirk. If direction doesn't change, it is used for buffer gathering.
In the case of regmap-i2c we remove the requirement for mangling as I2C_M_NOSTART is the only mangling feature which is being used. Signed-off-by: Mark Brown <redacted> --- Documentation/i2c/functionality | 1 + drivers/base/regmap/regmap-i2c.c | 2 +- drivers/i2c/algos/i2c-algo-bit.c | 2 +- drivers/i2c/algos/i2c-algo-pcf.c | 2 +- drivers/i2c/busses/i2c-nuc900.c | 3 ++- drivers/i2c/busses/i2c-s3c2410.c | 3 ++- drivers/input/joystick/as5011.c | 1 + drivers/video/matrox/matroxfb_maven.c | 1 + include/linux/i2c.h | 5 +++-- 9 files changed, 13 insertions(+), 7 deletions(-)
Review:
quoted hunk
diff --git a/Documentation/i2c/functionality b/Documentation/i2c/functionality index 42c17c1..fb2e77e 100644 --- a/Documentation/i2c/functionality +++ b/Documentation/i2c/functionality@@ -33,6 +33,7 @@ For the most up-to-date list of functionality constants, please check
You must also update the description of I2C_FUNC_PROTOCOL_MANGLING to no longer mention I2C_M_NOSTART.
I2C_FUNC_SMBUS_WRITE_BLOCK_DATA Handles the SMBus write_block_data command I2C_FUNC_SMBUS_READ_I2C_BLOCK Handles the SMBus read_i2c_block_data command I2C_FUNC_SMBUS_WRITE_I2C_BLOCK Handles the SMBus write_i2c_block_data command + I2C_FUNC_NOSTART Transfers can be sent without a start
Not true. Transfers always begin with a Start, even when I2C_M_NOSTART is used, because it is never set for the first message. I2C_FUNC_NOSTART means that messages other than the first may not get their usual Repeated Start and address prefix. So a better working IMHO would be: + I2C_FUNC_NOSTART Can skip repeated start sequence
quoted hunk
A few combinations of the above flags are also defined for your convenience:diff --git a/drivers/base/regmap/regmap-i2c.c b/drivers/base/regmap/regmap-i2c.c index 5f6b247..fa6bf52 100644 --- a/drivers/base/regmap/regmap-i2c.c +++ b/drivers/base/regmap/regmap-i2c.c@@ -42,7 +42,7 @@ static int regmap_i2c_gather_write(void *context, /* If the I2C controller can't do a gather tell the core, it * will substitute in a linear write for us. */ - if (!i2c_check_functionality(i2c->adapter, I2C_FUNC_PROTOCOL_MANGLING)) + if (!i2c_check_functionality(i2c->adapter, I2C_FUNC_NOSTART)) return -ENOTSUPP; xfer[0].addr = i2c->addr;diff --git a/drivers/i2c/algos/i2c-algo-bit.c b/drivers/i2c/algos/i2c-algo-bit.c index 7f0b832..fad22b0 100644 --- a/drivers/i2c/algos/i2c-algo-bit.c +++ b/drivers/i2c/algos/i2c-algo-bit.c@@ -608,7 +608,7 @@ bailout: static u32 bit_func(struct i2c_adapter *adap) { - return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | + return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_SMBUS_READ_BLOCK_DATA | I2C_FUNC_SMBUS_BLOCK_PROC_CALL | I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;diff --git a/drivers/i2c/algos/i2c-algo-pcf.c b/drivers/i2c/algos/i2c-algo-pcf.c index 5c23795..8b38986 100644 --- a/drivers/i2c/algos/i2c-algo-pcf.c +++ b/drivers/i2c/algos/i2c-algo-pcf.c@@ -401,7 +401,7 @@ out: static u32 pcf_func(struct i2c_adapter *adap) { - return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | + return I2C_FUNC_I2C | I2C_FUNC_NOSTART | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_PROTOCOL_MANGLING; }
A quick grep suggests that i2c-algo-pcf doesn't support I2C_M_NOSTART, only I2C_M_REV_DIR_ADDR. So you don't want to add I2C_FUNC_NOSTART to the functionality mask.
quoted hunk
diff --git a/drivers/i2c/busses/i2c-nuc900.c b/drivers/i2c/busses/i2c-nuc900.c index 03b6157..a26dfb8 100644 --- a/drivers/i2c/busses/i2c-nuc900.c +++ b/drivers/i2c/busses/i2c-nuc900.c@@ -502,7 +502,8 @@ static int nuc900_i2c_xfer(struct i2c_adapter *adap, /* declare our i2c functionality */ static u32 nuc900_i2c_func(struct i2c_adapter *adap) { - return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_PROTOCOL_MANGLING; + return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_NOSTART | + I2C_FUNC_PROTOCOL_MANGLING; } /* i2c bus registration info */diff --git a/drivers/i2c/busses/i2c-s3c2410.c b/drivers/i2c/busses/i2c-s3c2410.c index fa0b134..0195915 100644 --- a/drivers/i2c/busses/i2c-s3c2410.c +++ b/drivers/i2c/busses/i2c-s3c2410.c@@ -626,7 +626,8 @@ static int s3c24xx_i2c_xfer(struct i2c_adapter *adap, /* declare our i2c functionality */ static u32 s3c24xx_i2c_func(struct i2c_adapter *adap) { - return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_PROTOCOL_MANGLING; + return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_NOSTART | + I2C_FUNC_PROTOCOL_MANGLING; } /* i2c bus registration info */diff --git a/drivers/input/joystick/as5011.c b/drivers/input/joystick/as5011.c index 3063464..57d19d4 100644 --- a/drivers/input/joystick/as5011.c +++ b/drivers/input/joystick/as5011.c@@ -231,6 +231,7 @@ static int __devinit as5011_probe(struct i2c_client *client, } if (!i2c_check_functionality(client->adapter, + I2C_FUNC_NOSTART | I2C_FUNC_PROTOCOL_MANGLING)) { dev_err(&client->dev, "need i2c bus that supports protocol mangling\n");diff --git a/drivers/video/matrox/matroxfb_maven.c b/drivers/video/matrox/matroxfb_maven.c index 31b8f67..217678e 100644 --- a/drivers/video/matrox/matroxfb_maven.c +++ b/drivers/video/matrox/matroxfb_maven.c@@ -1243,6 +1243,7 @@ static int maven_probe(struct i2c_client *client, if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WRITE_WORD_DATA | I2C_FUNC_SMBUS_BYTE_DATA | + I2C_FUNC_NOSTART | I2C_FUNC_PROTOCOL_MANGLING)) goto ERROR0; if (!(data = kzalloc(sizeof(*data), GFP_KERNEL))) {diff --git a/include/linux/i2c.h b/include/linux/i2c.h index b66cb60..da46925 100644 --- a/include/linux/i2c.h +++ b/include/linux/i2c.h@@ -541,7 +541,7 @@ struct i2c_msg { __u16 flags; #define I2C_M_TEN 0x0010 /* this is a ten bit chip address */ #define I2C_M_RD 0x0001 /* read data, from slave to master */ -#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_PROTOCOL_MANGLING */ +#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_NOSTART */ #define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */ #define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */ #define I2C_M_NO_RD_ACK 0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */@@ -554,7 +554,7 @@ struct i2c_msg { #define I2C_FUNC_I2C 0x00000001 #define I2C_FUNC_10BIT_ADDR 0x00000002 -#define I2C_FUNC_PROTOCOL_MANGLING 0x00000004 /* I2C_M_NOSTART etc. */ +#define I2C_FUNC_PROTOCOL_MANGLING 0x00000004 /* I2C_M_IGNORE_NAK etc. */ #define I2C_FUNC_SMBUS_PEC 0x00000008 #define I2C_FUNC_SMBUS_BLOCK_PROC_CALL 0x00008000 /* SMBus 2.0 */ #define I2C_FUNC_SMBUS_QUICK 0x00010000@@ -569,6 +569,7 @@ struct i2c_msg { #define I2C_FUNC_SMBUS_WRITE_BLOCK_DATA 0x02000000 #define I2C_FUNC_SMBUS_READ_I2C_BLOCK 0x04000000 /* I2C-like block xfer */ #define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK 0x08000000 /* w/ 1-byte reg. addr. */ +#define I2C_FUNC_NOSTART 0x10000000 /* I2C_M_NOSTART */
Sorry for nitpicking but wouldn't I2C_FUNC_GATHER be a better name? NOSTART is an implementation detail now, the high level feature is the ability to gather multiple messages into one. Also I think I would prefer if you used 0x00000010 for the new functionality, so that it isn't too far away from I2C_FUNC_PROTOCOL_MANGLING.
#define I2C_FUNC_SMBUS_BYTE (I2C_FUNC_SMBUS_READ_BYTE | \ I2C_FUNC_SMBUS_WRITE_BYTE)
Thanks, -- Jean Delvare