From 11d4bb1bd067f9d01d18f620ccfad516dc579593 Mon Sep 17 00:00:00 2001 From: Fabio Estevam Date: Sat, 30 Nov 2013 15:24:42 +0100 Subject: [PATCH] ARM: 7907/1: lib: delay-loop: Add align directive to fix BogoMIPS calculation Currently mx53 (CortexA8) running at 1GHz reports: Calibrating delay loop... 663.55 BogoMIPS (lpj=3317760) Tom Evans verified that alignments of 0x0 and 0x8 run the two instructions of __loop_delay in one clock cycle (1 clock/loop), while alignments of 0x4 and 0xc take 3 clocks to run the loop twice. (1.5 clock/loop) The original object code looks like this: 00000010 <__loop_const_udelay>: 10: e3e01000 mvn r1, #0 14: e51f201c ldr r2, [pc, #-28] ; 0 <__loop_udelay-0x8> 18: e5922000 ldr r2, [r2] 1c: e0800921 add r0, r0, r1, lsr #18 20: e1a00720 lsr r0, r0, #14 24: e0822b21 add r2, r2, r1, lsr #22 28: e1a02522 lsr r2, r2, #10 2c: e0000092 mul r0, r2, r0 30: e0800d21 add r0, r0, r1, lsr #26 34: e1b00320 lsrs r0, r0, #6 38: 01a0f00e moveq pc, lr 0000003c <__loop_delay>: 3c: e2500001 subs r0, r0, #1 40: 8afffffe bhi 3c <__loop_delay> 44: e1a0f00e mov pc, lr After adding the 'align 3' directive to __loop_delay (align to 8 bytes): 00000010 <__loop_const_udelay>: 10: e3e01000 mvn r1, #0 14: e51f201c ldr r2, [pc, #-28] ; 0 <__loop_udelay-0x8> 18: e5922000 ldr r2, [r2] 1c: e0800921 add r0, r0, r1, lsr #18 20: e1a00720 lsr r0, r0, #14 24: e0822b21 add r2, r2, r1, lsr #22 28: e1a02522 lsr r2, r2, #10 2c: e0000092 mul r0, r2, r0 30: e0800d21 add r0, r0, r1, lsr #26 34: e1b00320 lsrs r0, r0, #6 38: 01a0f00e moveq pc, lr 3c: e320f000 nop {0} 00000040 <__loop_delay>: 40: e2500001 subs r0, r0, #1 44: 8afffffe bhi 40 <__loop_delay> 48: e1a0f00e mov pc, lr 4c: e320f000 nop {0} , which now reports: Calibrating delay loop... 996.14 BogoMIPS (lpj=4980736) Some more test results: On mx31 (ARM1136) running at 532 MHz, before the patch: Calibrating delay loop... 351.43 BogoMIPS (lpj=1757184) On mx31 (ARM1136) running at 532 MHz after the patch: Calibrating delay loop... 528.79 BogoMIPS (lpj=2643968) Also tested on mx6 (CortexA9) and on mx27 (ARM926), which shows the same BogoMIPS value before and after this patch. Reported-by: Tom Evans Suggested-by: Tom Evans Signed-off-by: Fabio Estevam Signed-off-by: Russell King --- arch/arm/lib/delay-loop.S | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm/lib/delay-loop.S b/arch/arm/lib/delay-loop.S index 36b668d8e121..bc1033b897b4 100644 --- a/arch/arm/lib/delay-loop.S +++ b/arch/arm/lib/delay-loop.S @@ -40,6 +40,7 @@ ENTRY(__loop_const_udelay) @ 0 <= r0 <= 0x7fffff06 /* * loops = r0 * HZ * loops_per_jiffy / 1000000 */ + .align 3 @ Delay routine ENTRY(__loop_delay) -- 2.20.1