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linux/include/asm-v850/rte_cb.h
H. Peter Anvin bdc807871d avoid overflows in kernel/time.c 
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>
2008-02-08 09:22:39 -08:00

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/*
* include/asm-v850/rte_cb.h -- Midas labs RTE-CB series of evaluation boards
*
* Copyright (C) 2001,02,03 NEC Electronics Corporation
* Copyright (C) 2001,02,03 Miles Bader <miles@gnu.org>
*
* This file is subject to the terms and conditions of the GNU General
* Public License. See the file COPYING in the main directory of this
* archive for more details.
*
* Written by Miles Bader <miles@gnu.org>
*/
#ifndef __V850_RTE_CB_H__
#define __V850_RTE_CB_H__
/* The SRAM on the Mother-A motherboard. */
#define MB_A_SRAM_ADDR GCS0_ADDR
#define MB_A_SRAM_SIZE 0x00200000 /* 2MB */
#ifdef CONFIG_RTE_GBUS_INT
/* GBUS interrupt support. */
# include <asm/gbus_int.h>
# define GBUS_INT_BASE_IRQ NUM_RTE_CB_IRQS
# define GBUS_INT_BASE_ADDR (GCS2_ADDR + 0x00006000)
/* Some specific interrupts. */
# define IRQ_MB_A_LAN IRQ_GBUS_INT(10)
# define IRQ_MB_A_PCI1(n) (IRQ_GBUS_INT(16) + (n))
# define IRQ_MB_A_PCI1_NUM 4
# define IRQ_MB_A_PCI2(n) (IRQ_GBUS_INT(20) + (n))
# define IRQ_MB_A_PCI2_NUM 4
# define IRQ_MB_A_EXT(n) (IRQ_GBUS_INT(24) + (n))
# define IRQ_MB_A_EXT_NUM 4
# define IRQ_MB_A_USB_OC(n) (IRQ_GBUS_INT(28) + (n))
# define IRQ_MB_A_USB_OC_NUM 2
# define IRQ_MB_A_PCMCIA_OC IRQ_GBUS_INT(30)
/* We define NUM_MACH_IRQS to include extra interrupts from the GBUS. */
# define NUM_MACH_IRQS (NUM_RTE_CB_IRQS + IRQ_GBUS_INT_NUM)
#else /* !CONFIG_RTE_GBUS_INT */
# define NUM_MACH_IRQS NUM_RTE_CB_IRQS
#endif /* CONFIG_RTE_GBUS_INT */
#ifdef CONFIG_RTE_MB_A_PCI
/* Mother-A PCI bus support. */
# include <asm/rte_mb_a_pci.h>
/* These are the base addresses used for allocating device address
space. 512K of the motherboard SRAM is in the same space, so we have
to be careful not to let it be allocated. */
# define PCIBIOS_MIN_MEM (MB_A_PCI_MEM_ADDR + 0x80000)
# define PCIBIOS_MIN_IO MB_A_PCI_IO_ADDR
/* As we don't really support PCI DMA to cpu memory, and use bounce-buffers
instead, perversely enough, this becomes always true! */
# define pci_dma_supported(dev, mask) 1
# define pcibios_assign_all_busses() 1
#endif /* CONFIG_RTE_MB_A_PCI */
#ifndef __ASSEMBLY__
extern void rte_cb_early_init (void);
extern void rte_cb_init_irqs (void);
#endif /* !__ASSEMBLY__ */
#endif /* __V850_RTE_CB_H__ */
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