bdc807871d
When the conversion factor between jiffies and milli- or microseconds is not a single multiply or divide, as for the case of HZ == 300, we currently do a multiply followed by a divide. The intervening result, however, is subject to overflows, especially since the fraction is not simplified (for HZ == 300, we multiply by 300 and divide by 1000). This is exposed to the user when passing a large timeout to poll(), for example. This patch replaces the multiply-divide with a reciprocal multiplication on 32-bit platforms. When the input is an unsigned long, there is no portable way to do this on 64-bit platforms there is no portable way to do this since it requires a 128-bit intermediate result (which gcc does support on 64-bit platforms but may generate libgcc calls, e.g. on 64-bit s390), but since the output is a 32-bit integer in the cases affected, just simplify the multiply-divide (*3/10 instead of *300/1000). The reciprocal multiply used can have off-by-one errors in the upper half of the valid output range. This could be avoided at the expense of having to deal with a potential 65-bit intermediate result. Since the intent is to avoid overflow problems and most of the other time conversions are only semiexact, the off-by-one errors were considered an acceptable tradeoff. At Ralf Baechle's suggestion, this version uses a Perl script to compute the necessary constants. We already have dependencies on Perl for kernel compiles. This does, however, require the Perl module Math::BigInt, which is included in the standard Perl distribution starting with version 5.8.0. In order to support older versions of Perl, include a table of canned constants in the script itself, and structure the script so that Math::BigInt isn't required if pulling values from said table. Running the script requires that the HZ value is available from the Makefile. Thus, this patch also adds the Kconfig variable CONFIG_HZ to the architectures which didn't already have it (alpha, cris, frv, h8300, m32r, m68k, m68knommu, sparc, v850, and xtensa.) It does *not* touch the sh or sh64 architectures, since Paul Mundt has dealt with those separately in the sh tree. Signed-off-by: H. Peter Anvin <hpa@zytor.com> Cc: Ralf Baechle <ralf@linux-mips.org>, Cc: Sam Ravnborg <sam@ravnborg.org>, Cc: Paul Mundt <lethal@linux-sh.org>, Cc: Richard Henderson <rth@twiddle.net>, Cc: Michael Starvik <starvik@axis.com>, Cc: David Howells <dhowells@redhat.com>, Cc: Yoshinori Sato <ysato@users.sourceforge.jp>, Cc: Hirokazu Takata <takata@linux-m32r.org>, Cc: Geert Uytterhoeven <geert@linux-m68k.org>, Cc: Roman Zippel <zippel@linux-m68k.org>, Cc: William L. Irwin <sparclinux@vger.kernel.org>, Cc: Chris Zankel <chris@zankel.net>, Cc: H. Peter Anvin <hpa@zytor.com>, Cc: Jan Engelhardt <jengelh@computergmbh.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
83 lines
2.4 KiB
C
83 lines
2.4 KiB
C
/*
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* include/asm-v850/fpga85e2c.h -- Machine-dependent defs for
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* FPGA implementation of V850E2/NA85E2C
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*
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* Copyright (C) 2002,03 NEC Electronics Corporation
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* Copyright (C) 2002,03 Miles Bader <miles@gnu.org>
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*
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* This file is subject to the terms and conditions of the GNU General
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* Public License. See the file COPYING in the main directory of this
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* archive for more details.
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*
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* Written by Miles Bader <miles@gnu.org>
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*/
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#ifndef __V850_FPGA85E2C_H__
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#define __V850_FPGA85E2C_H__
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#include <asm/v850e2.h>
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#include <asm/clinkage.h>
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#define CPU_MODEL "v850e2/fpga85e2c"
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#define CPU_MODEL_LONG "NEC V850E2/NA85E2C"
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#define PLATFORM "fpga85e2c"
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#define PLATFORM_LONG "NA85E2C FPGA implementation"
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/* `external ram'. */
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#define ERAM_ADDR 0
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#define ERAM_SIZE 0x00100000 /* 1MB */
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/* FPGA specific control registers. */
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/* Writing a non-zero value to FLGREG(0) will signal the controlling CPU
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to stop execution. */
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#define FLGREG_ADDR(n) (0xFFE80100 + 2*(n))
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#define FLGREG(n) (*(volatile unsigned char *)FLGREG_ADDR (n))
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#define FLGREG_NUM 2
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#define CSDEV_ADDR(n) (0xFFE80110 + 2*(n))
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#define CSDEV(n) (*(volatile unsigned char *)CSDEV_ADDR (n))
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/* Timer interrupts 0-3, interrupt at intervals from CLK/4096 to CLK/16384. */
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#define IRQ_RPU(n) (60 + (n))
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#define IRQ_RPU_NUM 4
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/* For <asm/irq.h> */
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#define NUM_CPU_IRQS 64
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/* General-purpose timer. */
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/* control/status register (can only be read/written via bit insns) */
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#define RPU_GTMC_ADDR 0xFFFFFB00
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#define RPU_GTMC (*(volatile unsigned char *)RPU_GTMC_ADDR)
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#define RPU_GTMC_CE_BIT 7 /* clock enable (control) */
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#define RPU_GTMC_OV_BIT 6 /* overflow (status) */
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#define RPU_GTMC_CLK_BIT 1 /* 0 = .5 MHz CLK, 1 = 1 Mhz (control) */
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/* 32-bit count (8 least-significant bits are always zero). */
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#define RPU_GTM_ADDR 0xFFFFFB28
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#define RPU_GTM (*(volatile unsigned long *)RPU_GTMC_ADDR)
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/* For <asm/page.h> */
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#define PAGE_OFFSET ERAM_ADDR /* minimum allocatable address */
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/* For <asm/entry.h> */
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/* `R0 RAM', used for a few miscellaneous variables that must be accessible
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using a load instruction relative to R0. The FPGA implementation
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actually has no on-chip RAM, so we use part of main ram just after the
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interrupt vectors. */
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#ifdef __ASSEMBLY__
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#define R0_RAM_ADDR lo(C_SYMBOL_NAME(_r0_ram))
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#else
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extern char _r0_ram;
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#define R0_RAM_ADDR ((unsigned long)&_r0_ram);
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#endif
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#endif /* __V850_FPGA85E2C_H__ */
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