a patch set
The PowerPC architecture is normally thought of as a big-endian domain -
the most significant byte of multi-byte values comes first. Big-endian is
consistent with a number of other architectures, but the fact that one
obscure architecture - x86 - is little-endian means that the world as a
whole tends toward the little-endian persuasion. As it happens, at least
some PowerPC processors can optionally be run in a little-endian mode. Ian
Munsie has posted
which enables Linux to take advantage of that feature and run little-endian
on suitably-equipped PowerPC processors.
The first question that came to the mind of a few reviewers was: "why?"
PowerPC runs fine as a big-endian architecture, and there has been little
clamor for little-endian support. Besides, endianness seems to be one of
those things that users can feel strongly about; to at least some PowerPC
users, little-endian apparently feels cheap, wrong, and PCish.
The answer, as expressed by Ben
Herrenschmidt, appears to be graphics hardware. A number of GPUs,
especially those aimed at embedded applications, only work in the
little-endian mode. Carefully-written device drivers can work around that
sort of limitation without too much trouble, but user-space code - which
often ends up talking to graphics hardware - is another story. Fixing all
of that code is not a task that anybody wants to take on. As a result,
PowerPC processors will not be considered for situations where
little-endian support is needed. Running the processor in little-endian
mode will nicely overcome that obstacle.
That said, it will take a little while before this support is generally
available. The kernel patches apparently look good, but there are
toolchain changes required which are not, yet, generally available. Until
that little issue is resolved, PowerPC will remain a club for big-endian
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