[U-Boot] [PATCH] mxs-i2c: Fix internal address byte order

[Marek Vasut]

Dear Torsten Fleischer,

> Dear Marek Vasut,
> 
> > > Large EEPROMs, e.g. 24lc32, need 2 byte to address the internal memory.
> > > These devices require that the high byte of the internal address has to
> > > be written first.
> > > The mxs_i2c driver currently writes the address' low byte first.
> > 
> > Are you sure about it? Are you sure what you're seeing isn't FIFO
> > overrun?
> 
> Yes, because I used 'i2c md' and 'i2c mw' for the test and these commands
> do only a small write transfer. They write 3 and 4 bytes respectively.
> This is in both cases only one FIFO word.
> 
> > Basically, how does your problem manifest? How did you test this?
> 
> First I wrote different bytes into the addresses 0x00 and 0x01 of the
> EEPROM using 'i2c mw', for example:
> 
> => i2c mw 54 0.2 12
> => i2c mw 54 1.2 34
> 
> Then I read the address range 0x00 - 0x01 and got:
> 
> => i2c md 54 0.2 2
> 0000: 12 ff    ..
> 
> That's not what I had expected. On address 0x01 there should be '34'
> instead of 'ff'.
> But when I read directly from the address 0x01 the command returned the
> correct value:
> 
> => i2c md 54 1.2 1
> 0001: 34    4
> 
> Thereupon I checked the I2C frame of the read and write commands to the
> address 0x01 with an oscilloscope. The scope showed that after the device's
> address the bytes 0x01 followed by 0x00 were sent to the EEPROM. But the
> two bytes must be in reverse order.
> 
> After inspecting the source code I swapped the address bytes, i.e. I used
> '100.2' instead of '1.2'. With it the read/write command accessed the
> address 0x01 of the EEPROM. I verified this with the scope.
> 
> Reading the range 0x00 - 0x01 returned then the expected content:
> 
> => i2c md 54 0.2 2
> 0000: 12 34    .4
> 
> I also tested the address byte swapping - before and after modifying the
> driver - with other addresses (e.g. 0x0180 and 0x0fff) by checking the I2C
> frames with the scope.
> After fixing the driver, I additionally read the whole EEPROM using 'i2c
> md' and verified the written addresses.

Oh this is very nice! Thanks a lot!

Obviously:
Acked-by: Marek Vasut <marex at denx.de>

> Best Regards
> Torsten Fleischer

Best regards,
Marek Vasut