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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
commit | 2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch) | |
tree | 848558de17fb3008cdf4d861b01ac7781903ce39 /arch/arc/include/asm/delay.h | |
parent | Initial commit. (diff) | |
download | linux-upstream.tar.xz linux-upstream.zip |
Adding upstream version 6.1.76.upstream/6.1.76upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | arch/arc/include/asm/delay.h | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/arch/arc/include/asm/delay.h b/arch/arc/include/asm/delay.h new file mode 100644 index 000000000..54db798f0 --- /dev/null +++ b/arch/arc/include/asm/delay.h @@ -0,0 +1,69 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) + * + * Delay routines using pre computed loops_per_jiffy value. + * + * vineetg: Feb 2012 + * -Rewrote in "C" to avoid dealing with availability of H/w MPY + * -Also reduced the num of MPY operations from 3 to 2 + * + * Amit Bhor: Codito Technologies 2004 + */ + +#ifndef __ASM_ARC_UDELAY_H +#define __ASM_ARC_UDELAY_H + +#include <asm-generic/types.h> +#include <asm/param.h> /* HZ */ + +extern unsigned long loops_per_jiffy; + +static inline void __delay(unsigned long loops) +{ + __asm__ __volatile__( + " mov lp_count, %0 \n" + " lp 1f \n" + " nop \n" + "1: \n" + : + : "r"(loops) + : "lp_count"); +} + +extern void __bad_udelay(void); + +/* + * Normal Math for computing loops in "N" usecs + * -we have precomputed @loops_per_jiffy + * -1 sec has HZ jiffies + * loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N) + * + * Approximate Division by multiplication: + * -Mathematically if we multiply and divide a number by same value the + * result remains unchanged: In this case, we use 2^32 + * -> (loops_per_N_usec * 2^32 ) / 2^32 + * -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32 + * -> (loops_per_jiffy * HZ * N * 4295) / 2^32 + * + * -Divide by 2^32 is very simply right shift by 32 + * -We simply need to ensure that the multiply per above eqn happens in + * 64-bit precision (if CPU doesn't support it - gcc can emaulate it) + */ + +static inline void __udelay(unsigned long usecs) +{ + unsigned long loops; + + /* (u64) cast ensures 64 bit MPY - real or emulated + * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops + */ + loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32; + + __delay(loops); +} + +#define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \ + : __udelay(n)) : __udelay(n)) + +#endif /* __ASM_ARC_UDELAY_H */ |