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89 lines
2.5 KiB
89 lines
2.5 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* |
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* Copyright (C) 2006 Jim Cromie |
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* |
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* This is a clocksource driver for the Geode SCx200's 1 or 27 MHz |
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* high-resolution timer. The Geode SC-1100 (at least) has a buggy |
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* time stamp counter (TSC), which loses time unless 'idle=poll' is |
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* given as a boot-arg. In its absence, the Generic Timekeeping code |
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* will detect and de-rate the bad TSC, allowing this timer to take |
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* over timekeeping duties. |
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* |
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* Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch) |
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*/ |
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#include <linux/clocksource.h> |
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#include <linux/init.h> |
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#include <linux/module.h> |
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#include <linux/ioport.h> |
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#include <linux/scx200.h> |
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#define NAME "scx200_hrt" |
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static int mhz27; |
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module_param(mhz27, int, 0); /* load time only */ |
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MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)"); |
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static int ppm; |
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module_param(ppm, int, 0); /* load time only */ |
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MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)"); |
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/* HiRes Timer configuration register address */ |
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#define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5) |
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/* and config settings */ |
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#define HR_TMEN (1 << 0) /* timer interrupt enable */ |
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#define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */ |
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#define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */ |
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/* The base timer frequency, * 27 if selected */ |
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#define HRT_FREQ 1000000 |
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static u64 read_hrt(struct clocksource *cs) |
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{ |
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/* Read the timer value */ |
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return (u64) inl(scx200_cb_base + SCx200_TIMER_OFFSET); |
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} |
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static struct clocksource cs_hrt = { |
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.name = "scx200_hrt", |
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.rating = 250, |
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.read = read_hrt, |
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.mask = CLOCKSOURCE_MASK(32), |
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.flags = CLOCK_SOURCE_IS_CONTINUOUS, |
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/* mult, shift are set based on mhz27 flag */ |
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}; |
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static int __init init_hrt_clocksource(void) |
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{ |
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u32 freq; |
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/* Make sure scx200 has initialized the configuration block */ |
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if (!scx200_cb_present()) |
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return -ENODEV; |
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/* Reserve the timer's ISA io-region for ourselves */ |
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if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET, |
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SCx200_TIMER_SIZE, |
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"NatSemi SCx200 High-Resolution Timer")) { |
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pr_warn("unable to lock timer region\n"); |
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return -ENODEV; |
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} |
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/* write timer config */ |
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outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0), |
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scx200_cb_base + SCx200_TMCNFG_OFFSET); |
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freq = (HRT_FREQ + ppm); |
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if (mhz27) |
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freq *= 27; |
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pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm); |
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return clocksource_register_hz(&cs_hrt, freq); |
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} |
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module_init(init_hrt_clocksource); |
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MODULE_AUTHOR("Jim Cromie <[email protected]>"); |
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MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer"); |
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MODULE_LICENSE("GPL");
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