Re: [Linaro-acpi] [PATCH] ARM: ACPI: remove 64bit divide replace with do_div

On 06/24/2013 09:01 AM, Graeme Gregory wrote:

From: Graeme Gregory graeme.gregory@linaro.org

I some situations custom 64bit by 32bit divide was giving the wrong values so replace it with the internal kernel do_div function instead.

Grumble. My apologies; I should have tested the divide more extensively rather that trust what I started with on the 'net.

Signed-off-by: Graeme Gregory graeme.gregory@linaro.org

arch/arm/include/asm/acpi.h | 18 ++--- drivers/acpi/plat/arm/Makefile | 1 - drivers/acpi/plat/arm/acpi_div_64_by_32.S | 105 ----------------------------- 3 files changed, 7 insertions(+), 117 deletions(-) delete mode 100644 drivers/acpi/plat/arm/acpi_div_64_by_32.S

diff --git a/arch/arm/include/asm/acpi.h b/arch/arm/include/asm/acpi.h index aafc276..e752c5c 100644 --- a/arch/arm/include/asm/acpi.h +++ b/arch/arm/include/asm/acpi.h @@ -31,6 +31,8 @@

#include <linux/init.h>

+#include <asm/div64.h>

• #define COMPILER_DEPENDENT_INT64 long long #define COMPILER_DEPENDENT_UINT64 unsigned long long

@@ -54,17 +56,11 @@ #define ACPI_ENABLE_IRQS() local_irq_enable() #define ACPI_FLUSH_CPU_CACHE() flush_cache_all()

-#define ACPI_DIV_64_BY_32(n_hi, n_lo, d32, q32, r32) \

• asm ("mov r0, %2\n" \

•     "mov	r1, %3\n"                       \
  

•     "mov	r2, %4\n"                       \
  

•         "bl        __arm_acpi_div_64_by_32\n"      \
  

•         "mov       %0, r0\n"                       \
  

•         "mov       %1, r1\n"                       \
  

•     : "=r"(q32), "=r"(r32)		/* output operands */   \
  

•     : "r"(n_hi), "r"(n_lo), "r"(d32)	/* input operands */    \
  

•     : "r0", "r1", "r2" 		/* clobbered registers */ \
  

•        )
  

+#define ACPI_DIV_64_BY_32(n_hi, n_lo, d32, q32, r32) { \

• u64 value = (u64)n_hi << 32 | n_lo; \
• r32 = do_div(value, d32); \
• q32 = value; \
• }

Ack'd. Not as fast, but speed is irrelevant for ARMv7 and AArch64 doesn't have the issue.

#define ACPI_SHIFT_RIGHT_64(n_hi, n_lo) \ asm ("mov r0, %2\n" \ diff --git a/drivers/acpi/plat/arm/Makefile b/drivers/acpi/plat/arm/Makefile index aa9dd19..a1f056d 100644 --- a/drivers/acpi/plat/arm/Makefile +++ b/drivers/acpi/plat/arm/Makefile @@ -1,4 +1,3 @@ obj-y += boot.o obj-y += sleep.o

-obj-$(CONFIG_ARM) += acpi_div_64_by_32.o diff --git a/drivers/acpi/plat/arm/acpi_div_64_by_32.S b/drivers/acpi/plat/arm/acpi_div_64_by_32.S deleted file mode 100644 index 573bce4..0000000 --- a/drivers/acpi/plat/arm/acpi_div_64_by_32.S +++ /dev/null @@ -1,105 +0,0 @@ -/*

• • Copyright (c) 2013, Al Stone ahs3@redhat.com
• • __acpi_arm_div64_by_32: perform integer division of a 64-bit value

• •                     a 32-bit value
    

• • The algorithm is borrowed from the GMP library, but has been redone
• • here in order to put this implementation under a GPLv2 license.
• • This program is free software; you can redistribute it and/or modify
• • it under the terms of the GNU General Public License as published by
• • the Free Software Foundation; either version 2 of the License, or
• • (at your option) any later version.
• • This program is distributed in the hope that it will be useful,
• • but WITHOUT ANY WARRANTY; without even the implied warranty of
• • MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
• • GNU General Public License for more details.
• • You should have received a copy of the GNU General Public License
• • along with this program; if not, write to the Free Software
• • Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
• */

-#ifdef __ARM_ARCH_7A__

-#include <linux/linkage.h>

-/*

• • This needs to be called in the following manner:

• •  n_lo    => r0           # these are the low 32 bits of the dividend
    

• •  n_hi    => r1           # the high 32 bits of the dividend
    

• •  d32     => r2           # the 32-bit divisor
    

• • The result is:

• •  q32     <= r0           # the 32-bit quotient
    

• •  r32     <= r1           # the 32-bit remainder
    

• • This should be consistent with the normal ARMv7 calling conventions.
• */

-ENTRY(__arm_acpi_div_64_by_32)

•    mov     r12, #32                // loop counter
  

•    cmp     r2, #0x80000000         // check divisor MSB and clear carry
  

•    bcs     bigdiv
  

-loop: adcs r1, r1, r1 // handle each bit

•    adc     r0, r0, r0
  

•    cmp     r0, r2
  

•    subcs   r0, r0, r2
  

•    sub     r12, r12, #1
  

•    teq     r12, #0
  

•    bne     loop
  

•    mov     r3, r0                  // stash the remainder for a tic
  

•    adc     r0, r1, r1              // quotient: add in last carry
  

•    mov     r1, r3                  // remainder (now in right register)
  

•    mov     pc, lr
  

-bigdiv: stmfd sp!, { r8, lr } // clear some scratch space

•    and     r8, r1, #1              // save LSB of dividend
  

•    mov     lr, r0, lsl #31
  

•    orrs    r1, lr, r1, lsr #1      // r1 = lower part >> 1 bit
  

•    mov     r0, r0, lsr #1          // r0 = higher part >> 1 bit
  

•    and     lr, r2, #1              // save LSB of divisor
  

•    movs    r2, r2, lsr #1          // r2 = floor(divisor / 2)
  

•    adc     r2, r2, #0              // r2 = ceil(divisor / 2)
  

-loop2: adcs r1, r1, r1 // handle each bit

•    adc     r0, r0, r0
  

•    cmp     r0, r2
  

•    subcs   r0, r0, r2
  

•    sub     r12, r12, #1
  

•    teq     r12, #0
  

•    bne     loop2
  

•    adc     r1, r1, r1              // shift and add last carry
  

•    add     r0, r8, r0, lsl #1      // shift in remaining dividend LSB
  

•    tst     lr, lr
  

•    beq     evendiv
  

•    rsb     r2, lr, r2, lsl #1      // restore divisor value
  

•    adds    r0, r0, r1              // adjust for omitted divisor LSB
  

•    addcs   r1, r1, #1              // adjust quotient if a carry results
  

•    subcs   r0, r0, r2              // adjust remainder, if carry
  

•    cmp     r0, r2
  

•    subcs   r0, r0, #1              // adjust remainder
  

•    addcs   r1, r1, #1              // adjust quotient
  

-evendiv:

•    mov     r3, r0                  // stash the remainder for a tic
  

•    mov     r0, r1                  // quotient
  

•    mov     r1, r3                  // remainder
  

•    ldmfd   sp!, { r8, pc }         // restore the registers used
  

-ENDPROC(__arm_acpi_div_64_by_32)

-#else /* ! __ARM_ARCH_7A__ */ -#error __arm_acpi_div_64_by_32 not defined for this architecture -#endif