Hi, Am 28.10.2012 17:33, schrieb Jean Delvare: > Hi Frank, > > On Sun, 28 Oct 2012 15:32:16 +0200, Frank Schäfer wrote: >> Am 28.10.2012 14:03, schrieb Jean Delvare: >>> On Sat, 27 Oct 2012 18:41:19 +0300, Frank Schäfer wrote: >>>> What are the correct functionality flags to use in this case ? >>>> I2C_FUNC_I2C | I2C_FUNC_SMBUS_READ_BYTE | I2C_FUNC_SMBUS_WRITE_WORD_DATA ? >>> If your controller is limited then I2C_FUNC_I2C is most certainly >>> wrong. From what you described, I'd say: >>> >>> I2C_FUNC_SMBUS_READ_BYTE | I2C_FUNC_SMBUS_WRITE_BYTE_DATA >>> >>> This doesn't match what Laurent said about SCCB 4 months ago though: >>> >>> "The read transaction transmits 2 2-byte messages (addr/w, reg, >>> followed by addr/r, data)." >>> >>> You can take a look at Documentation/i2c/smbus-protocol to match >>> transactions to function names (and from there to I2C_FUNC flags.) >> Ok, I've been digging deeper into this but still don't understand the >> meaning of the functionality flags I2C_FUNC_*** with regards to the >> capabilites of an master_xfer implemetation in struct i2c_algortihm... >> Are they supposed to describe the smbus operations/methods that can be >> successfully emulated by the smbus layer using i2c_xfer or do they >> describe the actual capabilities of function master_xfer / the i2c adapter ? > Most I2C_FUNC_* flags actual refer to the smbus_xfer method. A driver > implementing master_xfer is typically fully I2C capable and can thus > run almost any I2C or SMBus transaction. Such a driver will set > functionality flags to I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL. The rest of > the flags are for SMBus-only controllers. Each flag basically > corresponds to an i2c_smbus_*() function, which in turn corresponds to > the combination of an SMBus transaction type or size and a direction > (read or write). > > The mapping between i2c_smbus_*() functions and functionality flags is > rather obvious, but for clarity I'll update > Documentation/i2c/smbus-protocol to mention it. Patch follows. > > Also see Documentation/i2c/functionality for a detailed explanation of > how functionality flags work both on the I2C/SMBus adapter driver and > the I2C device driver sides. Ok, so the functionality flags describe whats possible when using the smbus functions. That's a bit confusing/misleading if the adapter driver doesn't implement the smbus_xfer function in struct i2c_algorithm. And if the i2c adapter / master_xfer fcn has some restrictions (e.g. data length), things are getting complicated. I2C_FUNC_SMBUS functionality flags are sufficiently documented, but what about I2C_FUNC_I2C ? Should this be set always if there is a master_xfer function or only if the adapter is fully i2c compliant (and what does "fully i2c compliant" mean ?) ? To summarize: there is no possibilty to determine the maximum i2c data length when using the i2c_xfer functions directly. It's basically try and error and if the message is too long, the adapters should return -EOPNOTSUPP. Thanks for your explanations, Frank -- 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
