riscv: Using TOOLCHAIN_HAS_ZIHINTPAUSE marco replace zihintpause

Actually it is a part of Conor's
commit aae538cd03bc ("riscv: fix detection of toolchain
Zihintpause support").
It is looks like a merge issue. Samuel's
commit 0b1d60d6dd9e ("riscv: Fix build with
CONFIG_CC_OPTIMIZE_FOR_SIZE=y") do not base on Conor's commit and
revert to __riscv_zihintpause. So this patch can fix it.

Signed-off-by: Minda Chen <minda.chen@starfivetech.com>
Fixes: 3c349eacc559 ("Merge patch "riscv: Fix build with CONFIG_CC_OPTIMIZE_FOR_SIZE=y"")
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230802064215.31111-1-minda.chen@starfivetech.com
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

riscv: cpu_relax: switch to riscv_has_extension_likely()

Switch cpu_relax() from static branch to the new helper
riscv_has_extension_likely()

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230128172856.3814-12-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

riscv: Fix build with CONFIG_CC_OPTIMIZE_FOR_SIZE=y

commit 8eb060e10185 ("arch/riscv: add Zihintpause support") broke
building with CONFIG_CC_OPTIMIZE_FOR_SIZE enabled (gcc 11.1.0):

CC arch/riscv/kernel/vdso/vgettimeofday.o
In file included from <command-line>:
./arch/riscv/include/asm/jump_label.h: In function 'cpu_relax':
././include/linux/compiler_types.h:285:33: warning: 'asm' operand 0 probably does not match constraints
285 | #define asm_volatile_goto(x...) asm goto(x)
| ^~~
./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro 'asm_volatile_goto'
41 | asm_volatile_goto(
| ^~~~~~~~~~~~~~~~~
././include/linux/compiler_types.h:285:33: error: impossible constraint in 'asm'
285 | #define asm_volatile_goto(x...) asm goto(x)
| ^~~
./arch/riscv/include/asm/jump_label.h:41:9: note: in expansion of macro 'asm_volatile_goto'
41 | asm_volatile_goto(
| ^~~~~~~~~~~~~~~~~
make[1]: *** [scripts/Makefile.build:249: arch/riscv/kernel/vdso/vgettimeofday.o] Error 1
make: *** [arch/riscv/Makefile:128: vdso_prepare] Error 2

Having a static branch in cpu_relax() is problematic because that
function is widely inlined, including in some quite complex functions
like in the VDSO. A quick measurement shows this static branch is
responsible by itself for around 40% of the jump table.

Drop the static branch, which ends up being the same number of
instructions anyway. If Zihintpause is supported, we trade the nop from
the static branch for a div. If Zihintpause is unsupported, we trade the
jump from the static branch for (what gets interpreted as) a nop.

Fixes: 8eb060e10185 ("arch/riscv: add Zihintpause support")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

riscv: fix detection of toolchain Zihintpause support

It is not sufficient to check if a toolchain supports a particular
extension without checking if the linker supports that extension
too. For example, Clang 15 supports Zihintpause but GNU bintutils
2.35.2 does not, leading build errors like so:

riscv64-linux-gnu-ld: -march=rv64i2p0_m2p0_a2p0_c2p0_zihintpause2p0: Invalid or unknown z ISA extension: 'zihintpause'

Add a TOOLCHAIN_HAS_ZIHINTPAUSE which checks if each of the compiler,
assembler and linker support the extension. Replace the ifdef in the
vdso with one depending on this new symbol.

Fixes: 8eb060e10185 ("arch/riscv: add Zihintpause support")
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20221006173520.1785507-3-conor@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv: add Zihintpause support

Implement support for the ZiHintPause extension.

The PAUSE instruction is a HINT that indicates the current hart’s rate
of instruction retirement should be temporarily reduced or paused.

Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Dao Lu <daolu@rivosinc.com>
[Palmer: Some minor merge conflicts.]
Link: https://lore.kernel.org/all/20220620201530.3929352-1-daolu@rivosinc.com/
Link: https://lore.kernel.org/all/20220811053356.17375-1-palmer@rivosinc.com/
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

RISC-V: fix barrier() use in <vdso/processor.h>

riscv's <vdso/processor.h> uses barrier() so it should include
<asm/barrier.h>

Fixes this build error:
CC [M] drivers/net/ethernet/emulex/benet/be_main.o
In file included from ./include/vdso/processor.h:10,
from ./arch/riscv/include/asm/processor.h:11,
from ./include/linux/prefetch.h:15,
from drivers/net/ethernet/emulex/benet/be_main.c:14:
./arch/riscv/include/asm/vdso/processor.h: In function 'cpu_relax':
./arch/riscv/include/asm/vdso/processor.h:14:2: error: implicit declaration of function 'barrier' [-Werror=implicit-function-declaration]
14 | barrier();

This happens with a total of 5 networking drivers -- they all use
<linux/prefetch.h>.

rv64 allmodconfig now builds cleanly after this patch.

Fixes fallout from:
815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive")

Fixes: ad5d1122b82f ("riscv: use vDSO common flow to reduce the latency of the time-related functions")
Reported-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

riscv: use vDSO common flow to reduce the latency of the time-related functions

Even if RISC-V has supported the vDSO feature, the latency of the functions
for obtaining the system time is still expensive. It is because these
functions still trigger a corresponding system call in the process, which
slows down the response time. If we want to remove the system call to
reduce the latency, the kernel should have the ability to output the system
clock information to userspace. This patch introduces the vDSO common flow
to enable the kernel to achieve the above feature and uses "rdtime"
instruction to obtain the current time in the user space. Under this
condition, the latency cost by the ecall from U-mode to S-mode can be
eliminated. After applying this patch, the latency of gettimeofday()
measured on the HiFive unleashed board can be reduced by %61.

Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>