Commit Graph

24264 Commits

Author SHA1 Message Date
Paul Mackerras
ff2e6d7e27 powerpc: Fix goof in 6xx and POWER4 idle power-save functions
This fixes a mistake I made when editing these functions - when I
took out the interrupt disabling code (because interrupts are now
disabled by the caller) I left the register that is used for the MSR
value to be used during doze/nap uninitialized.  This fixes it.

Also updated some of the comments in idle_power4.S and removed some
code that was copied over from idle_6xx.S but is no longer relevant
(we don't ever clear the CPU_FTR_CAN_NAP bit at runtime for POWER4).

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-28 09:28:14 +11:00
Paul Mackerras
9618edab82 powerpc: Fix event-scan code for 32-bit CHRP
On CHRP machines we are supposed to call into firmware (RTAS)
periodically, to give it a chance to check for errors and other
events.  Under ppc we had some special code in timer_interrupt
to do this, but that didn't get transferred over to arch/powerpc.
Instead, we use an array of timer_list structs, one per CPU,
and use add_timer_on to make sure each one gets called on the
appropriate CPU.

With this we can remove the heartbeat_* elements of the ppc_md
struct.

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 21:48:57 +11:00
Paul Mackerras
d0cc0dfa2d ppc: Remove duplicate exports of __down, __up etc.
__down, __down_interruptible and __up are defined and exported in
arch/powerpc/kernel/semaphore.c, and used from there for ARCH=ppc,
so there is no need to export them in arch/ppc/kernel/ppc_ksyms.c.

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 20:31:44 +11:00
Paul Mackerras
e7e2d2da26 powerpc: Don't compile in arch/ppc/kernel for 32-bit ARCH=powerpc
All of the things needed for 32-bit ARCH=powerpc builds have now
moved to arch/powerpc/kernel, so we don't need to go down into
arch/ppc/kernel any more, and we can remove the CONFIG_PPC_MERGE
conditional from arch/ppc/kernel/Makefile.

There were two files still referenced in the merge section of
arch/ppc/kernel/Makefile: ppc-stub.o, depending on CONFIG_KGDB,
and dma-mapping.o, depending on CONFIG_NOT_COHERENT_CACHE.  None
of the platforms currently in ARCH=powerpc have caches that
aren't coherent with DMA, but when we do get one we'll move
dma-mapping.c over.  As for CONFIG_KGDB, none of the Kconfig
files in the tree define it, so I'll let it languish for now.

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 20:17:06 +11:00
Paul Mackerras
8b844dd759 powerpc: Move perfmon_fsl_booke.c over to arch/powerpc
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 20:09:04 +11:00
Paul Mackerras
ed981856ca powerpc: Move module.c over to arch/powerpc
... and rename it to module_32.c since it is the 32-bit version.
The 32-bit and 64-bit ABIs are sufficiently different that having
a merged version isn't really practical.

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 19:28:58 +11:00
Paul Mackerras
45320bcbab powerpc: Move swsusp.S over to arch/powerpc
... and rename it to swsusp_32.S, since it's 32-bit only at this stage.

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 19:21:46 +11:00
Paul Mackerras
9b781727fd powerpc: Move cpu_setup_6xx.S and temp.c over to arch/powerpc
Also renamed temp.c to tau_6xx.c (for thermal assist unit) and updated
the Kconfig option description and help text for CONFIG_TAU.

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 19:15:26 +11:00
Paul Mackerras
0eb4cb9b16 powerpc: Move l2cr.S over to arch/powerpc
No functional changes, but call it l2cr_6xx.S since it is specific
to 6xx-family (including G3/750 and G4/74xx) processors.

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 15:22:28 +11:00
Paul Mackerras
fbd7740fdf powerpc: Simplify pSeries idle loop
Since pSeries only wants to do something different in the idle loop when
there is no work to do, we can simplify the code by implementing
ppc_md.power_save functions instead of complete idle loops.  There are
two versions: one for shared-processor partitions and one for dedicated-
processor partitions.

With this we also do a cede_processor() call on dedicated processor
partitions if the poll_pending() call indicates that the hypervisor
has work it wants to do.

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 15:06:20 +11:00
Paul Mackerras
a0652fc9a2 powerpc: Unify the 32 and 64 bit idle loops
This unifies the 32-bit (ARCH=ppc and ARCH=powerpc) and 64-bit idle
loops.  It brings over the concept of having a ppc_md.power_save
function from 32-bit to ARCH=powerpc, which lets us get rid of
native_idle().  With this we will also be able to simplify the idle
handling for pSeries and cell.

Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 15:03:03 +11:00
Michael Neuling
55aab8cd3a [PATCH] powerpc: HVC init race
I've been hitting a crash on boot where tty_open is being called before the
hvc console driver setup is complete.  This fixes the problem.

Thanks to benh for his help on this.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Acked-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:49:48 +11:00
Sylvain Munaut
1f5e3b028c [PATCH] ppc32: Reorganize and complete MPC52xx initial cpu setup
ppc32: Reorganize and complete MPC52xx initial cpu setup

This patch splits up the CPU setup into a generic part and a
platform specific part. We also add a few missing init at the
same time.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:49:00 +11:00
Sylvain Munaut
f8dd311982 [PATCH] ppc32: Adds support for the LITE5200B dev board
ppc32: Adds support for the LITE5200B dev board

This LITE5200B devboard is the new development board for the
Freescale MPC5200 processor. It has two PCI slots and so a
different PCI IRQ routing.

Signed-off-by: John Rigby <jrigby@freescale.com>
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:58 +11:00
Sylvain Munaut
5931c43500 [PATCH] ppc32: Adds support for the PCI hostbridge in MPC5200B
ppc32: Adds support for the PCI hostbridge in MPC5200B

Signed-off-by: John Rigby <jrigby@freescale.com>
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:56 +11:00
Michael Neuling
37a801c776 [PATCH] powerpc: legacy_serial loop cleanup
We only ever execute the loop once, so let's move it to a function
making it more readable.  Cleanup patch, no functional change.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:54 +11:00
Anton Blanchard
b8c7b976a5 [PATCH] powerpc: Compile warning in hvcs driver
We ended up with an unused variable after the tty updates went in. Fix it.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:52 +11:00
Anton Blanchard
c258dd40ab [PATCH] powerpc: Consistent printing of node id
We were printing node ids in hex in one spot. Lets be consistent and
always print them in decimal.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:50 +11:00
Anton Blanchard
4df20460a3 [PATCH] powerpc: Allow non zero boot cpuids
We currently have a hack to flip the boot cpu and its secondary thread
to logical cpuid 0 and 1. This means the logical - physical mapping will
differ depending on which cpu is boot cpu. This is most apparent on
kexec, where we might kexec on any cpu and therefore change the mapping
from boot to boot.

The patch below does a first pass early on to work out the logical cpuid
of the boot thread. We then fix up some paca structures to match.

Ive also removed the boot_cpuid_phys variable for ppc64, to be
consistent we use get_hard_smp_processor_id(boot_cpuid) everywhere.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:48 +11:00
Linas Vepstas
b4f382a3e5 [PATCH] powerpc/pseries: Cleanup device name printing.
This avoids printk'ing a NULL string.

Signed-off-by: Linas Vepstas <linas@linas.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:46 +11:00
Arnd Bergmann
79c227a92c [PATCH] spufs: Fix endless protection fault on LS writes by SPE.
If an SPE attempts a DMA put to a local store after already doing
a get, the kernel must update the HW PTE to allow the write access.
This case was not being handled correctly.

From: Mike Kistler <mkistler@us.ibm.com>
Signed-off-by: Mike Kistler <mkistler@us.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:44 +11:00
Arnd Bergmann
47952d5ea6 [PATCH] powerpc: use guarded ioremap for cell on-chip mappings
I'm not sure where the information came from, but I assumed
that doing cache-inhibited mappings for mmio regions was
sufficient.

It seems we also need the guarded bit set, like everyone
else, which is the default for ioremap.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:42 +11:00
Arnd Bergmann
2fa68747da [PATCH] powerpc: fix spider-pic affinity setting
As noticed by Milton Miller, setting the initial affinity in
spider-pic can go wrong if the target node field was not orinally
empty.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:40 +11:00
John Rose
16cc11daff [PATCH] powerpc: dynamic probe - use ppc_md.pci_probe_mode()
Change the dynamic PCI probe function for pSeries to use
ppc_md.pci_probe_mode() when appropriate.

Signed-off-by: John Rose <johnrose@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:38 +11:00
Olaf Hering
add60ef303 [PATCH] powerpc: return to OF via trap, not exit
Do not call prom exit prom_panic. It clears the screen and the exit
message is lost.

On some (or all?) pmacs it causes another crash when OF tries to print
the date and time in its banner.

Set of_platform earlier to catch more prom_panic() calls.

Signed-off-by: Olaf Hering <olh@suse.de>
Acked-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:36 +11:00
Andrew Morton
069007ae07 [PATCH] powerpc: hot_add_scn_to_nid() build fix
The return statement is to prevent `warning: 'nid' might be used uninitialized
in this function'.

Cc: Nathan Lynch <nathanl@austin.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:34 +11:00
Olaf Hering
6088857b16 [PATCH] correct the comment about stackpointer alignment in __boot_from_prom
The address of variable val in prom_init_stdout is passed to prom_getprop.
prom_getprop casts the pointer to u32 and passes it to call_prom in the hope
that OpenFirmware stores something there.
But the pointer is truncated in the lower bits and the expected value is
stored somewhere else.

In my testing I had a stackpointer of 0x0023e6b4. val was at offset 120,
wich has address 0x0023e72c. But the value passed to OF was 0x0023e728.

c00000000040b710:       3b 01 00 78     addi    r24,r1,120
...
c00000000040b754:       57 08 00 38     rlwinm  r8,r24,0,0,28
...
c00000000040b784:       80 01 00 78     lwz     r0,120(r1)
...
c00000000040b798:       90 1b 00 0c     stw     r0,12(r27)
...

The stackpointer came from 32bit code.
The chain was yaboot -> zImage -> vmlinux

PowerMac OpenFirmware does appearently not handle the ELF sections
correctly.  If yaboot was compiled in
/usr/src/packages/BUILD/lilo-10.1.1/yaboot, then the stackpointer is
unaligned. But the stackpointer is correct if yaboot is compiled in
/tmp/yaboot.

This bug triggered since 2.6.15, now prom_getprop is an inline
function. gcc clears the lower bits, instead of just clearing the
upper 32 bits.

Signed-off-by: Olaf Hering <olh@suse.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:32 +11:00
Dirk Herrendoerfer
ca3e91cb0c [PATCH] spufs: initialize context correctly
the mfc member of a new context was not initialized to zero,
which potentially leads to wild memory accesses.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:30 +11:00
Mark Nutter
6df10a82f8 [PATCH] spufs: enable SPE problem state MMIO access.
This patch is layered on top of CONFIG_SPARSEMEM
and is patterned after direct mapping of LS.

This patch allows mmap() of the following regions:
"mfc", which represents the area from [0x3000 - 0x3fff];
"cntl", which represents the area from [0x4000 - 0x4fff];
"signal1" which begins at offset 0x14000; "signal2" which
begins at offset 0x1c000.

The signal1 & signal2 files may be mmap()'d by regular user
processes.  The cntl and mfc file, on the other hand, may
only be accessed if the owning process has CAP_SYS_RAWIO,
because they have the potential to confuse the kernel
with regard to parallel access to the same files with
regular file operations: the kernel always holds a spinlock
when accessing registers in these areas to serialize them,
which can not be guaranteed with user mmaps,

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:28 +11:00
Arnd Bergmann
a33a7d7309 [PATCH] spufs: implement mfc access for PPE-side DMA
This patch adds a new file called 'mfc' to each spufs directory.
The file accepts DMA commands that are a subset of what would
be legal DMA commands for problem state register access. Upon
reading the file, a bitmask is returned with the completed
tag groups set.

The file is meant to be used from an abstraction in libspe
that is added by a different patch.

From the kernel perspective, this means a process can now
offload a memory copy from or into an SPE local store
without having to run code on the SPE itself.

The transfer will only be performed while the SPE is owned
by one thread that is waiting in the spu_run system call
and the data will be transferred into that thread's
address space, independent of which thread started the
transfer.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:26 +11:00
Arnd Bergmann
2dd14934c9 [PATCH] spufs: allow SPU code to do syscalls
An SPU does not have a way to implement system calls
itself, but it can create intercepts to the kernel.

This patch uses the method defined by the JSRE interface
for C99 host library calls from an SPU to implement
Linux system calls. It uses the reserved SPU stop code
0x2104 for this, using the structure layout and syscall
numbers for ppc64-linux.

I'm still undecided wether it is better to have a list
of allowed syscalls or a list of forbidden syscalls,
since we can't allow an SPU to call all syscalls that
are defined for ppc64-linux.

This patch implements the easier choice of them, with a
blacklist that only prevents an SPU from calling anything
that interacts with its own execution, e.g fork, execve,
clone, vfork, exit, spu_run and spu_create and everything
that deals with signals.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:24 +11:00
Arnd Bergmann
a7f31841a4 [PATCH] powerpc: declare arch syscalls in <asm/syscalls.h>
powerpc currently declares some of its own system calls
in <asm/unistd.h>, but not all of them. That place also
contains remainders of the now almost unused kernel syscall
hack.

 - Add a new <asm/syscalls.h> with clean declarations
 - Include that file from every source that implements one
   of these
 - Get rid of old declarations in <asm/unistd.h>

This patch is required as a base for implementing system
calls from an SPU, but also makes sense as a general
cleanup.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:22 +11:00
Arnd Bergmann
5536408c21 [PATCH] powerpc: work around a cell interrupt HW bug
Apparently we have found a bug in the CPU that causes
external interrupts to sometimes get disabled indefinitely.
This adds a workaround for the problem.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:20 +11:00
Jens Osterkamp
d0e57c6837 [PATCH] powerpc: cell interrupt controller updates
The current interrupt controller setup on Cell is done
in a rather ad-hoc way with device tree properties
that are not standardized at all.

In an attempt to do something that follows the OF standard
(or at least the IBM extensions to it) more closely,
we have now come up with this patch. It still provides
a fallback to the old behaviour when we find older firmware,
that hack can not be removed until the existing customer
installations have upgraded.

Cc: hpenner@de.ibm.com
Cc: stk@de.ibm.com
Cc: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Milton Miller <miltonm@bga.com>
Cc: benh@kernel.crashing.org
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:18 +11:00
Arnd Bergmann
1a19f85584 [PATCH] powerpc: update cell defconfig
The default configuration in mainline got a little out of
sync with what we use internally.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:16 +11:00
Arnd Bergmann
5fa500bfc6 [PATCH] powerpc: fix cell iommu setup
A small bug crept in the iommu driver when we made it more
generic. This patch is needed for boards that have a dma
window that does not start at bus address zero.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:14 +11:00
Michael Ellerman
dd4d7bfad6 [PATCH] powerpc: Change firmware_has_feature() to a macro
So that we can use firmware_has_feature() in a BUG_ON() and have the compiler
elide the code entirely if the feature can never be set, change
firmware_has_feature to a macro. Unfortunate, but necessary at least until
GCC bug #26724 is fixed.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:12 +11:00
Michael Ellerman
e3f94b85f9 [PATCH] powerpc: Make BUG_ON & WARN_ON play nice with compile-time optimisations
Change BUG_ON and WARN_ON to give the compiler a chance to perform
compile-time optimsations. Depending on the complexity of the condition,
the compiler may not do this very well, so if it's important check the
object code.

Current GCC's (4.x) produce good code as long as the condition does not
include a function call, including a static inline.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:10 +11:00
Stephen Rothwell
af308377e2 [PATCH] powerpc: fix various sparse warnings
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:08 +11:00
Stephen Rothwell
7c92943c7b [PATCH] powerpc: work around sparse warnings in cputable.h
Christoph noticed that sparse warned about all the enum tags in cuptable.h
that had values that required them to be type log. (enum tags are ints
according to the standard.)

This patch attempts to fix them in the least intrusive way possible by
turning them all into #defines except for the 32 bit CPU_FTRS_POSSIBLE and
CPU_FTRS_ALWAYS which are hard to construct that way.  This works because
these last two contain no bits above 2^31.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-03-27 14:48:06 +11:00
David S. Miller
5d5d7727a8 [SPARC64]: Kill duplicate exports of string library functions.
Kbuild now points these out.

Signed-off-by: David S. Miller <davem@davemloft.net>
2006-03-26 15:30:29 -08:00
David S. Miller
e7104b6704 [SPARC64]: Update defconfig.
Signed-off-by: David S. Miller <davem@davemloft.net>
2006-03-26 14:58:40 -08:00
Manfred Spraul
64bc0430ee [PATCH] one ipc/sem.c->mutex.c converstion too many..
Ingo's sem2mutex patch incorrectly replaced one reference to ipc/sem.c
with ipc/mutex.c in a comment.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-26 09:46:36 -08:00
Linus Torvalds
9ae21d1bb3 Merge git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial
* git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial:
  drivers/char/ftape/lowlevel/fdc-io.c: Correct a comment
  Kconfig help: MTD_JEDECPROBE already supports Intel
  Remove ugly debugging stuff
  do_mounts.c: Minor ROOT_DEV comment cleanup
  BUG_ON() Conversion in drivers/s390/block/dasd_devmap.c
  BUG_ON() Conversion in mm/mempool.c
  BUG_ON() Conversion in mm/memory.c
  BUG_ON() Conversion in kernel/fork.c
  BUG_ON() Conversion in ipc/sem.c
  BUG_ON() Conversion in fs/ext2/
  BUG_ON() Conversion in fs/hfs/
  BUG_ON() Conversion in fs/dcache.c
  BUG_ON() Conversion in fs/buffer.c
  BUG_ON() Conversion in input/serio/hp_sdc_mlc.c
  BUG_ON() Conversion in md/dm-table.c
  BUG_ON() Conversion in md/dm-path-selector.c
  BUG_ON() Conversion in drivers/isdn
  BUG_ON() Conversion in drivers/char
  BUG_ON() Conversion in drivers/mtd/
2006-03-26 09:41:18 -08:00
Bastien Roucaries
e9415777b1 drivers/char/ftape/lowlevel/fdc-io.c: Correct a comment
This patch correct a comment about cli().

Signed-off-by: Bastien Roucaries <roucaries.bastien@gmail.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
2006-03-26 19:18:07 +02:00
Adrian Bunk
8917f6f70b Kconfig help: MTD_JEDECPROBE already supports Intel
Intel chips are already supported.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Acked-by: David Woodhouse <dwmw2@infradead.org>
2006-03-26 19:15:03 +02:00
Akinobu Mita
f9b4192923 [PATCH] bitops: hweight() speedup
<linux@horizon.com> wrote:

This is an extremely well-known technique.  You can see a similar version that
uses a multiply for the last few steps at
http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel whch
refers to "Software Optimization Guide for AMD Athlon 64 and Opteron
Processors"
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/25112.PDF

It's section 8.6, "Efficient Implementation of Population-Count Function in
32-bit Mode", pages 179-180.

It uses the name that I am more familiar with, "popcount" (population count),
although "Hamming weight" also makes sense.

Anyway, the proof of correctness proceeds as follows:

	b = a - ((a >> 1) & 0x55555555);
	c = (b & 0x33333333) + ((b >> 2) & 0x33333333);
	d = (c + (c >> 4)) & 0x0f0f0f0f;
#if SLOW_MULTIPLY
	e = d + (d >> 8)
	f = e + (e >> 16);
	return f & 63;
#else
	/* Useful if multiply takes at most 4 cycles */
	return (d * 0x01010101) >> 24;
#endif

The input value a can be thought of as 32 1-bit fields each holding their own
hamming weight.  Now look at it as 16 2-bit fields.  Each 2-bit field a1..a0
has the value 2*a1 + a0.  This can be converted into the hamming weight of the
2-bit field a1+a0 by subtracting a1.

That's what the (a >> 1) & mask subtraction does.  Since there can be no
borrows, you can just do it all at once.

Enumerating the 4 possible cases:

0b00 = 0  ->  0 - 0 = 0
0b01 = 1  ->  1 - 0 = 1
0b10 = 2  ->  2 - 1 = 1
0b11 = 3  ->  3 - 1 = 2

The next step consists of breaking up b (made of 16 2-bir fields) into
even and odd halves and adding them into 4-bit fields.  Since the largest
possible sum is 2+2 = 4, which will not fit into a 4-bit field, the 2-bit
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                          "which will not fit into a 2-bit field"

fields have to be masked before they are added.

After this point, the masking can be delayed.  Each 4-bit field holds a
population count from 0..4, taking at most 3 bits.  These numbers can be added
without overflowing a 4-bit field, so we can compute c + (c >> 4), and only
then mask off the unwanted bits.

This produces d, a number of 4 8-bit fields, each in the range 0..8.  From
this point, we can shift and add d multiple times without overflowing an 8-bit
field, and only do a final mask at the end.

The number to mask with has to be at least 63 (so that 32 on't be truncated),
but can also be 128 or 255.  The x86 has a special encoding for signed
immediate byte values -128..127, so the value of 255 is slower.  On other
processors, a special "sign extend byte" instruction might be faster.

On a processor with fast integer multiplies (Athlon but not P4), you can
reduce the final few serially dependent instructions to a single integer
multiply.  Consider d to be 3 8-bit values d3, d2, d1 and d0, each in the
range 0..8.  The multiply forms the partial products:

	           d3 d2 d1 d0
	        d3 d2 d1 d0
	     d3 d2 d1 d0
	+ d3 d2 d1 d0
	----------------------
	           e3 e2 e1 e0

Where e3 = d3 + d2 + d1 + d0.   e2, e1 and e0 obviously cannot generate
any carries.

Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-26 08:59:30 -08:00
Artem B. Bityuckiy
3be7d29fb9 Remove ugly debugging stuff
Signed-off-by: Adrian Bunk <bunk@stusta.de>
2006-03-26 18:58:31 +02:00
Akinobu Mita
37d54111c1 [PATCH] bitops: hweight() related cleanup
By defining generic hweight*() routines

- hweight64() will be defined on all architectures
- hweight_long() will use architecture optimized hweight32() or hweight64()

I found two possible cleanups by these reasons.

Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-26 08:57:15 -08:00
Akinobu Mita
e9bebd6f3a [PATCH] bitops: remove unused generic bitops in include/linux/bitops.h
generic_{ffs,fls,fls64,hweight{64,32,16,8}}() were moved into
include/asm-generic/bitops.h.  So all architectures don't use them.

Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-26 08:57:15 -08:00