Re: [Qemu-devel] [PATCH for-1.4] libi2c-omap: Fix endianness dependency

[Andreas Färber]

Am 05.02.2013 17:58, schrieb Anthony Liguori:
> Andreas Färber <address@hidden> writes:
> 
>>          memread(s->addr + OMAP_I2C_DATA, &data, 2);
>>  
>> -        memread(s->addr + OMAP_I2C_STAT, &stat, 2);
>> +        omap_i2c_read16(s->addr + OMAP_I2C_STAT, &stat);
>>          if (unlikely(len == 1)) {
>> -            *buf = data & 0xf;
>> +            *buf = le16_to_cpu(data) & 0xf;
> 
> I don't really get this part.  You're effectively unswapping the bytes,
> right?

No. I am reading into "data" unswapped above. This line swaps "data"
when only half of the register is used for the 0xF mask, which assumes
host endianness - I can re-test tonight to verify whether it breaks without.

Probably I should insert a white line to make the "data" vs. "stat"
distinction more clear.
I was using a broken STAT register bit before, if you check the
libi2c-omap patch history, where we couldn't agree on how to fix
properly without spec. Thus I changed the condition to not rely on stat;
reading the register seemed necessary though.

Alternatively the I2C device has a Big Endian bit that we could enable -
but I would rather not have the tests run different device code paths
based on host.

Regards,
Andreas

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