[U-Boot] [PATCH] p1022ds: fix switching of DIU/LBC signals

[Timur Tabi <timur@freescale.com>]

Wood Scott-B07421 wrote:
> 
> Careful with the barriers.
> 
> You've got a raw readback, which means it's not going to wait for
> completion with the twi/isync hack.

You told me that since I'm doing a read following a write to uncached memory,
that I don't need a sync.

And what twi/isync hack are you talking about?  The one in in_8?

> 
> Ordinarily that would be OK, since you only need ordering between the
> readb and the first access in set_mux_to_diu().  Unfortunately, that
> first access is an 8-bit access, which for some strange reason does
> sync differently than 16/32-bit accesses.  The latter do sync+write,
> but 8-bit does write+eieio.  So there's no barrier between the read
> and the write.

Wait, I don't understand.  Where are you getting this from?  What do you mean by
16-bit accesses does sync+write vs. write+eieio?  Where is the sync/eieio coming
from?

As for why I don't use in_8, etc, it's because I'm trying to optimize this code.
 Unlike Dave's code, this stuff needs to be as fast as possible.  Although, I
wonder if an extra sync will make a difference considering the overhead of
switching the muxes.

-- 
Timur Tabi
Linux kernel developer at Freescale