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Maciej W. Rozycki d2abb95bb1 MIPS: Reinstate platform `__div64_32' handler 
commit c49f71f607 upstream.

Our current MIPS platform `__div64_32' handler is inactive, because it
is incorrectly only enabled for 64-bit configurations, for which generic
`do_div' code does not call it anyway.

The handler is not suitable for being called from there though as it
only calculates 32 bits of the quotient under the assumption the 64-bit
divident has been suitably reduced.  Code for such reduction used to be
there, however it has been incorrectly removed with commit c21004cd5b
("MIPS: Rewrite <asm/div64.h> to work with gcc 4.4.0."), which should
have only updated an obsoleted constraint for an inline asm involving
$hi and $lo register outputs, while possibly wiring the original MIPS
variant of the `do_div' macro as `__div64_32' handler for the generic
`do_div' implementation

Correct the handler as follows then:

- Revert most of the commit referred, however retaining the current
  formatting, except for the final two instructions of the inline asm
  sequence, which the original commit missed.  Omit the original 64-bit
  parts though.

- Rename the original `do_div' macro to `__div64_32'.  Use the combined
  `x' constraint referring to the MD accumulator as a whole, replacing
  the original individual `h' and `l' constraints used for $hi and $lo
  registers respectively, of which `h' has been obsoleted with GCC 4.4.
  Update surrounding code accordingly.

  We have since removed support for GCC versions before 4.9, so no need
  for a special arrangement here; GCC has supported the `x' constraint
  since forever anyway, or at least going back to 1991.

- Rename the `__base' local variable in `__div64_32' to `__radix' to
  avoid a conflict with a local variable in `do_div'.

- Actually enable this code for 32-bit rather than 64-bit configurations
  by qualifying it with BITS_PER_LONG being 32 instead of 64.  Include
  <asm/bitsperlong.h> for this macro rather than <linux/types.h> as we
  don't need anything else.

- Finally include <asm-generic/div64.h> last rather than first.

This has passed correctness verification with test_div64 and reduced the
module's average execution time down to 1.0668s and 0.2629s from 2.1529s
and 0.5647s respectively for an R3400 CPU @40MHz and a 5Kc CPU @160MHz.
For a reference 64-bit `do_div' code where we have the DDIVU instruction
available to do the whole calculation right away averages at 0.0660s for
the latter CPU.

Fixes: c21004cd5b ("MIPS: Rewrite <asm/div64.h> to work with gcc 4.4.0.")
Reported-by: Huacai Chen <chenhuacai@kernel.org>
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Cc: stable@vger.kernel.org # v2.6.30+
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2021-05-19 10:13:17 +02:00
arch
block blk-mq: Swap two calls in blk_mq_exit_queue() 2021-05-19 10:13:14 +02:00
certs certs: Fix blacklist flag type confusion 2021-03-04 11:37:59 +01:00
crypto async_xor: increase src_offs when dropping destination page 2021-05-14 09:49:59 +02:00
Documentation kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
drivers iommu/vt-d: Remove WO permissions on second-level paging entries 2021-05-19 10:13:17 +02:00
fs f2fs: compress: fix to assign cc.cluster_idx correctly 2021-05-19 10:13:14 +02:00
include mm: fix struct page layout on 32-bit systems 2021-05-19 10:13:17 +02:00
init seccomp: Fix CONFIG tests for Seccomp_filters 2021-05-14 09:50:24 +02:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel kernel/resource: make walk_mem_res() find all busy IORESOURCE_MEM resources 2021-05-19 10:13:09 +02:00
lib kasan: fix unit tests with CONFIG_UBSAN_LOCAL_BOUNDS enabled 2021-05-19 10:13:11 +02:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm/hugetlb: fix F_SEAL_FUTURE_WRITE 2021-05-19 10:13:11 +02:00
net mm: fix struct page layout on 32-bit systems 2021-05-19 10:13:17 +02:00
samples samples/bpf: Fix broken tracex1 due to kprobe argument change 2021-05-19 10:12:57 +02:00
scripts kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
security KEYS: trusted: Fix memory leak on object td 2021-05-19 10:12:50 +02:00
sound ASoC: rt286: Make RT286_SET_GPIO_* readable and writable 2021-05-19 10:13:00 +02:00
tools perf tools: Fix dynamic libbpf link 2021-05-19 10:13:13 +02:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt kvm: exit halt polling on need_resched() as well 2021-05-19 10:13:12 +02:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS f2fs: move ioctl interface definitions to separated file 2021-05-19 10:13:00 +02:00
Makefile kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.