Re: 10-bit address support

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

On Thu, 10 Nov 2011 07:58:35 -0800, Jeffrey (Sheng-Hui) Chu wrote:
> 
> 
> > -----Original Message-----
> > From: Jean Delvare [mailto:khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org]
> > Sent: Thursday, November 10, 2011 10:08 AM
> > To: Linux I2C
> > Cc: Jeffrey (Sheng-Hui) Chu
> > Subject: 10-bit address support
> > 
> > Hi all,
> > 
> > After Sheng-Hui's fix to i2c-algo-bit, it would seem that we are almost
> > there with 10-bit slave address support. There's one remaining thing
> > that worries me though: the 7-bit and 10-bit address spaces overlap.
> > From Documentation/i2c/ten-bit-addresses:
> > 
> > "The sets of addresses do not intersect: the 7 bit address 0x10 is not
> > the same as the 10 bit address 0x10 (though a single device could
> > respond to both of them)."
> 
> From my understanding of the spec, there is no overlap.  
> The 10-bit client at 0x10 will be addressed by the following address sequence:
> 0Xf0 0X10 <data-out>  or 0xf0 0x10 <restart> 0xf1<data-in>
> 
> The 7-bit client at 0x10 will be addressed by the following address sequence:
> 0x20 <data-out>  or 0x21 <data-in>
> 
> 0xf0 is equivalent to 7-bit address of 0x78 which is a reserved address in 7-bit space.  A compliant 7-bit client should not use or respond to this address.

what you wrote above is completely exact, but is also completely
unrelated to what I explained. The overlapping that currently exists is
in the device names inside the kernel. It's a pure software issue.

> Don't need to do any workaround. IMHO

I'm certain we do.

-- 
Jean Delvare