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| author |   Paul Burton <paul.burton@mips.com> | 2018-08-07 10:15:04 -0700 |
|---|---|---|
| committer | Paul Burton <paul.burton@mips.com> | 2018-08-07 10:33:45 -0700 |
| commit | 36dc5b20e31db5cd470eb1934815320e7a0434c3 (patch) | |
| tree | 118a47c62d73c07c0caad4006fce201bc070f385 /arch/mips | |
| parent | MIPS: Use read-write output operand in __write_64bit_c0_split() (diff) | |
| download | linux-dev-36dc5b20e31db5cd470eb1934815320e7a0434c3.tar.xz linux-dev-36dc5b20e31db5cd470eb1934815320e7a0434c3.zip | |
MIPS: Use dins to simplify __write_64bit_c0_split()
The code in __write_64bit_c0_split() is used by MIPS32 kernels running
on MIPS64 CPUs to write a 64-bit value to a 64-bit coprocessor 0
register using a single 64-bit dmtc0 instruction. It does this by
combining the 2x 32-bit registers used to hold the 64-bit value into a
single register, which in the existing code involves three steps:
1) Zero extend register A which holds bits 31:0 of our data, since it
may have previously held a sign-extended value.
2) Shift register B which holds bits 63:32 of our data in bits 31:0
left by 32 bits, such that the bits forming our data are in the
position they'll be in the final 64-bit value & bits 31:0 of the
register are zero.
3) Or the two registers together to form the 64-bit value in one
64-bit register.
From MIPS r2 onwards we have a dins instruction which can effectively
perform all 3 of those steps using a single instruction.
Add a path for MIPS r2 & beyond which uses dins to take bits 31:0 from
register B & insert them into bits 63:32 of register A, giving us our
full 64-bit value in register A with one instruction.
Since we know that MIPS r2 & above support the sel field for the dmtc0
instruction, we don't bother special casing sel==0. Omiting the sel
field would assemble to exactly the same instruction as when we
explicitly specify that it equals zero.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Diffstat (limited to 'arch/mips')
| -rw-r--r-- | arch/mips/include/asm/mipsregs.h | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h index dd46ab2a4ffd..a3ee982b4c1a 100644 --- a/arch/mips/include/asm/mipsregs.h +++ b/arch/mips/include/asm/mipsregs.h @@ -16,6 +16,7 @@ #include <linux/linkage.h> #include <linux/types.h> #include <asm/hazards.h> +#include <asm/isa-rev.h> #include <asm/war.h> /* @@ -1489,7 +1490,15 @@ do { \ unsigned long __flags; \ \ local_irq_save(__flags); \ - if (sel == 0) \ + if (MIPS_ISA_REV >= 2) \ + __asm__ __volatile__( \ + ".set\tpush\n\t" \ + ".set\t" MIPS_ISA_LEVEL "\n\t" \ + "dins\t%L0, %M0, 32, 32\n\t" \ + "dmtc0\t%L0, " #source ", " #sel "\n\t" \ + ".set\tpop" \ + : "+r" (__tmp)); \ + else if (sel == 0) \ __asm__ __volatile__( \ ".set\tmips64\n\t" \ "dsll\t%L0, %L0, 32\n\t" \ |