Mark A. Greer wrote: > Jean Delvare wrote: > >>> Don't the i2c_smbus_[read|write]_word_data() routines pass the u16 >>> data in little endian format because that's the endian of the SMbus? >> >> Not exactly. The bytes arrive LSB first, but the i2c bus drivers then >> convert the word to the endianess of the system. At least they are >> supposed to, those who don't are broken, if any. >> >>> Surely if swab16() is used rather than cpu_to_le16(), different values >>> are passed to the xxx_word_data() routines depending on cpu endian? >> >> No, since the conversion is done by the bus drivers. The only reason why >> swab16 is used is because the chips do not respect the SMBus specs (with >> good reasons, but still...) >> > Uhh oh... The i2c-mv64xxx.c driver--note that the ctlr is *not* and > smbus ctlr and only provides one byte at a time to the driver--that I > wrote simply puts the incoming bytes into the buffer in the order that > they arrive (and sends them out in the order that they appear in the > buffer (i.e., as a byte-stream)). That is wrong?!?! This was what was confusing me too. As I understand it now (Jean please correct me if I'm wrong) the core code behind the smbus read/write word_data() routines presents the u16 value as a little endian value. If the chip driver knows the chip implements 16-bit registers as big endian then it must swap the bytes, regardless of cpu endian. I don't think Jean's statement that "the conversion is done by the bus drivers" is true, but maybe I still don't understand... :) > So, after the read transfer is completed, I should go thru the buffer > applying le16_to_cpu() to each pair of bytes? What if there are an odd > number of bytes? Also, I guess I should apply cpu_to_le16() to the > buffer before I send it out? I don't see how a bus driver can do this when all it has is a single "xfer" routine to transfer a byte stream. I already have a driver that reads 8 bytes from consecutive byte-wide registers as an 8-byte transfer. Just because the byte stream has more than one byte, we can't endian-convert byte pairs... /james
