On 10 August 2015 at 09:26, Crt Mori <cmo@xxxxxxxxxxx> wrote: > On 9 August 2015 at 09:40, Wolfram Sang <wsa@xxxxxxxxxxxxx> wrote: >> On Fri, Jul 24, 2015 at 03:20:42PM +0200, Crt Mori wrote: >>> If you want to send more than 1 byte as command to slave you need to go away >>> from the smbus (which has a 8 bit command defined in specification). i2c has >>> no such limitation in specification and since we want to have a longer than >>> 1 byte command, we need additional function to handle it. With outside >>> buffers we have also avoided endianness problems (if we would just define a >>> u16 command instead of u8). Also there are now no limitations (as per i2c >>> specification) of command length. >>> Addressed read function is when we have a slave device which accepts commands >>> longer than byte or some subcommands in same write string before issuing a >>> repeat start before read cycle to read more than byte (or byte) from slave >>> device. >>> >>> Signed-off-by: Crt Mori <cmo@xxxxxxxxxxx> >> >> I don't see much gain over using i2c_transfer directly to be honest. Do >> you see much use of that in the kernel? Any other gain I missed? And if >> at all, the function should be probably named i2c_write_then_read or >> something. >> > This debate is what I wanted to have. The new Melexis sensor will be > using it and > since I think some others might also be using it in future I would > rather put it to > i2c. It is more i2c command than sensor specific so I think it fits into i2c. > > Another gain is that when number of functions each device does increase, as > well as ram/rom addressing read commands with longer than 8-bit register read > commands will be needed. Especially since most sensors have digital design of > i2c interface (not software) which means native access to registers is required, > therefor 8bit read addressing (smbus) might not be suitable. > > I can fix the function name, but in core this is a master read command. > For example IIO list just got the driver for ms_sensors [1] which uses the same function. I am sure we can find more. [1] http://www.spinics.net/lists/linux-iio/msg19925.html >>> --- >>> drivers/i2c/i2c-core.c | 40 ++++++++++++++++++++++++++++++++++++++++ >>> include/linux/i2c.h | 4 ++++ >>> 2 files changed, 44 insertions(+) >>> >>> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c >>> index 069a41f..bccf83f 100644 >>> --- a/drivers/i2c/i2c-core.c >>> +++ b/drivers/i2c/i2c-core.c >>> @@ -2980,6 +2980,46 @@ int i2c_slave_unregister(struct i2c_client *client) >>> EXPORT_SYMBOL_GPL(i2c_slave_unregister); >>> #endif >>> >>> +/** >>> + * i2c_addressed_read - writes read commands with desired length and read >>> + * desired length of data. >>> + * @client: Handle to slave device >>> + * @command: Pointer to command location >>> + * @cmd_len: Number of command bytes on command location >>> + * @data: Pointer to read data location >>> + * @data_len: Expected number of read bytes >>> + * >>> + * Addressed read on slave device when command is longer than byte. Returns >>> + * negative errno on error and 0 on success. >>> + */ >>> +s32 i2c_addressed_read(const struct i2c_client *client, u8 *command, >>> + u16 cmd_len, u8 *data, u16 data_len) >>> +{ >>> + s32 status; >>> + struct i2c_msg msg[2] = { >>> + { >>> + .addr = client->addr, >>> + .flags = client->flags, >>> + .len = cmd_len, >>> + .buf = command, >>> + }, >>> + { >>> + .addr = client->addr, >>> + .flags = client->flags | I2C_M_RD, >>> + .len = data_len, >>> + .buf = data, >>> + }, >>> + }; >>> + >>> + status = i2c_transfer(client->adapter, msg, 2); >>> + >>> + if (status < 0) >>> + return status; >>> + >>> + return 0; >>> +} >>> +EXPORT_SYMBOL(i2c_addressed_read); >>> + >>> MODULE_AUTHOR("Simon G. Vogl <simon@xxxxxxxxxxxxxxxxx>"); >>> MODULE_DESCRIPTION("I2C-Bus main module"); >>> MODULE_LICENSE("GPL"); >>> diff --git a/include/linux/i2c.h b/include/linux/i2c.h >>> index e83a738..d3cc1af 100644 >>> --- a/include/linux/i2c.h >>> +++ b/include/linux/i2c.h >>> @@ -121,6 +121,10 @@ extern s32 i2c_smbus_read_i2c_block_data(const struct i2c_client *client, >>> extern s32 i2c_smbus_write_i2c_block_data(const struct i2c_client *client, >>> u8 command, u8 length, >>> const u8 *values); >>> + >>> +s32 i2c_addressed_read(const struct i2c_client *client, u8 *command, >>> + u16 cmd_len, u8 *data, u16 data_len); >>> + >>> #endif /* I2C */ >>> >>> /** >>> -- >>> 2.1.4 >>> -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
