Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.4 11/23] ARC: udelay: fix inline assembler by adding LP_COUNT to clobber list | Date | Tue, 31 Jan 2017 06:37:13 +0100 |
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4.4-stable review patch. If anyone has any objections, please let me know.
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From: Vineet Gupta <vgupta@synopsys.com>
commit 36425cd67052e3becf325fd4d3ba5691791ef7e4 upstream.
commit 3c7c7a2fc8811bc ("ARC: Don't use "+l" inline asm constraint") modified the inline assembly to setup LP_COUNT register manually and NOT rely on gcc to do it (with the +l inline assembler contraint hint, now being retired in the compiler)
However the fix was flawed as we didn't add LP_COUNT to asm clobber list, meaning gcc doesn't know that LP_COUNT or zero-delay-loops are in action in the inline asm.
This resulted in some fun - as nested ZOL loops were being generared
| mov lp_count,250000 ;16 # tmp235, | lp .L__GCC__LP14 # <======= OUTER LOOP (gcc generated) | .L14: | ld r2, [r5] # MEM[(volatile u32 *)prephitmp_43], w | dmb 1 | breq r2, -1, @.L21 #, w,, | bbit0 r2,1,@.L13 # w,, | ld r4,[r7] ;25 # loops_per_jiffy, loops_per_jiffy | mpymu r3,r4,r6 #, loops_per_jiffy, tmp234 | | mov lp_count, r3 # <====== INNER LOOP (from inline asm) | lp 1f | nop | 1: | nop_s | .L__GCC__LP14: ; loop end, start is @.L14 #,
This caused issues with drivers relying on sane behaviour of udelay friends.
With LP_COUNT added to clobber list, gcc doesn't generate the outer loop in say above case.
Addresses STAR 9001146134
Reported-by: Joao Pinto <jpinto@synopsys.com> Fixes: 3c7c7a2fc8811bc ("ARC: Don't use "+l" inline asm constraint") Signed-off-by: Vineet Gupta <vgupta@synopsys.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- arch/arc/include/asm/delay.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/arch/arc/include/asm/delay.h +++ b/arch/arc/include/asm/delay.h @@ -26,7 +26,9 @@ static inline void __delay(unsigned long " lp 1f \n" " nop \n" "1: \n" - : : "r"(loops)); + : + : "r"(loops) + : "lp_count"); } extern void __bad_udelay(void);
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