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Maciej W. Rozycki da72e7f8cc MIPS: Avoid handcoded DIVU in `__div64_32' altogether 
commit 25ab14cbe9 upstream.

Remove the inline asm with a DIVU instruction from `__div64_32' and use
plain C code for the intended DIVMOD calculation instead.  GCC is smart
enough to know that both the quotient and the remainder are calculated
with single DIVU, so with ISAs up to R5 the same instruction is actually
produced with overall similar code.

For R6 compiled code will work, but separate DIVU and MODU instructions
will be produced, which are also interlocked, so scalar implementations
will likely not perform as well as older ISAs with their asynchronous MD
unit.  Likely still faster then the generic algorithm though.

This removes a compilation error for R6 however where the original DIVU
instruction is not supported anymore and the MDU accumulator registers
have been removed and consequently GCC complains as to a constraint it
cannot find a register for:

In file included from ./include/linux/math.h:5,
                 from ./include/linux/kernel.h:13,
                 from mm/page-writeback.c:15:
./include/linux/math64.h: In function 'div_u64_rem':
./arch/mips/include/asm/div64.h:76:17: error: inconsistent operand constraints in an 'asm'
   76 |                 __asm__("divu   $0, %z1, %z2"                           \
      |                 ^~~~~~~
./include/asm-generic/div64.h:245:25: note: in expansion of macro '__div64_32'
  245 |                 __rem = __div64_32(&(n), __base);       \
      |                         ^~~~~~~~~~
./include/linux/math64.h:91:22: note: in expansion of macro 'do_div'
   91 |         *remainder = do_div(dividend, divisor);
      |                      ^~~~~~

This has passed correctness verification with test_div64 and reduced the
module's average execution time down to 1.0404s from 1.0445s with R3400
@40MHz.  The module's MIPS I machine code has also shrunk by 12 bytes or
3 instructions.

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-05-22 10:57:41 +02:00
arch MIPS: Avoid handcoded DIVU in `__div64_32' altogether 2021-05-22 10:57:41 +02:00
block blk-mq: Swap two calls in blk_mq_exit_queue() 2021-05-22 10:57:40 +02:00
certs certs: Fix blacklist flag type confusion 2021-03-03 18:22:46 +01:00
crypto crypto: api - check for ERR pointers in crypto_destroy_tfm() 2021-05-22 10:57:16 +02:00
Documentation sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output 2021-03-07 11:27:45 +01:00
drivers FDDI: defxx: Make MMIO the configuration default except for EISA 2021-05-22 10:57:41 +02:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:20:30 +01:00
fs squashfs: fix divide error in calculate_skip() 2021-05-22 10:57:39 +02:00
include smp: Fix smp_call_function_single_async prototype 2021-05-22 10:57:35 +02:00
init init/Kconfig: make COMPILE_TEST depend on HAS_IOMEM 2021-04-10 13:20:12 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:17:07 +02:00
kernel kernel: kexec_file: fix error return code of kexec_calculate_store_digests() 2021-05-22 10:57:39 +02:00
lib net: fix nla_strcmp to handle more then one trailing null character 2021-05-22 10:57:39 +02:00
mm userfaultfd: release page in error path to avoid BUG_ON 2021-05-22 10:57:39 +02:00
net netfilter: nftables: avoid overflows in nft_hash_buckets() 2021-05-22 10:57:39 +02:00
samples samples/bpf: Fix broken tracex1 due to kprobe argument change 2021-05-22 10:57:37 +02:00
scripts kconfig: nconf: stop endless search loops 2021-05-22 10:57:37 +02:00
security security: commoncap: fix -Wstringop-overread warning 2021-05-22 10:57:21 +02:00
sound ASoC: rt286: Make RT286_SET_GPIO_* readable and writable 2021-05-22 10:57:37 +02:00
tools selftests: Set CC to clang in lib.mk if LLVM is set 2021-05-22 10:57:36 +02:00
usr initramfs: restore default compression behavior 2020-04-13 10:34:19 +02:00
virt KVM: arm64: Fix exclusive limit for IPA size 2021-03-17 16:34:35 +01:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 16:36:12 +01:00
Makefile Linux 4.14.232 2021-04-28 12:08:44 +02:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

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

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

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.