forked from rubenslte/android_kernel_samsung_msm8226
Matt Wagantall
d1f5ad7543
Presently, small timeout values will round up to 1 jiffy which, on CONFIG_HZ=100 systems, corresponds to a full 10 milliseconds. This is undesirable for drivers specifying timeouts of only a few 10's of microseconds (which is common), since they may end up tight-loop spinning for hundreds or thousands of times longer than expected before reporting a timeout. Additionally, jiffies cannot be reliably used with time_after() when the value of jiffies is small (like 1). In rare but real scenarios, jiffies may actually increment by more than 1 at a time. Specifically, this will occur if interrupts are disabled on for more than 1 jiffy (10 milliseconds for CONFIG_HZ=100) on the CPU responsible for incrementing jiffies. If interrupts are re-enabled on that CPU between the time the iopoll code (on another CPU) calculates the timeout value of jiffies and when the time_after() comparison is made, then the iopoll APIs may return -ETIMEDOUT prematurely, even though the specified timeout has not actually expired. Using ktime_get() avoid this problem (which arguably also needs a generic fix to avoid similar problems for other code which use jiffies to calculate timeouts). CRs-Fixed: 587801 Change-Id: I19150f41965b918c59c3fb98e29a8bd2e2c9609f Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
115 lines
3.7 KiB
C
115 lines
3.7 KiB
C
/*
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* Copyright (c) 2012-2014 The Linux Foundation. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 and
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* only version 2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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*/
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#ifndef _LINUX_IOPOLL_H
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#define _LINUX_IOPOLL_H
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#include <linux/kernel.h>
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#include <linux/types.h>
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#include <linux/hrtimer.h>
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#include <linux/delay.h>
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#include <asm-generic/errno.h>
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#include <asm/io.h>
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/**
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* readl_poll_timeout - Periodically poll an address until a condition is met or a timeout occurs
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* @addr: Address to poll
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* @val: Variable to read the value into
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* @cond: Break condition (usually involving @val)
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* @sleep_us: Maximum time to sleep between reads in uS (0 tight-loops)
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* @timeout_us: Timeout in uS, 0 means never timeout
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*
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* Returns 0 on success and -ETIMEDOUT upon a timeout. In either
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* case, the last read value at @addr is stored in @val. Must not
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* be called from atomic context if sleep_us or timeout_us are used.
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*/
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#define readl_poll_timeout(addr, val, cond, sleep_us, timeout_us) \
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({ \
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ktime_t timeout = ktime_add_us(ktime_get(), timeout_us); \
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might_sleep_if(timeout_us); \
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for (;;) { \
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(val) = readl(addr); \
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if (cond) \
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break; \
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if (timeout_us && ktime_compare(ktime_get(), timeout) > 0) { \
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(val) = readl(addr); \
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break; \
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} \
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if (sleep_us) \
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usleep_range(DIV_ROUND_UP(sleep_us, 4), sleep_us); \
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} \
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(cond) ? 0 : -ETIMEDOUT; \
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})
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/**
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* readl_poll_timeout_noirq - Periodically poll an address until a condition is met or a timeout occurs
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* @addr: Address to poll
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* @val: Variable to read the value into
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* @cond: Break condition (usually involving @val)
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* @max_reads: Maximum number of reads before giving up
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* @time_between_us: Time to udelay() between successive reads
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*
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* Returns 0 on success and -ETIMEDOUT upon a timeout.
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*/
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#define readl_poll_timeout_noirq(addr, val, cond, max_reads, time_between_us) \
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({ \
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int count; \
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for (count = (max_reads); count > 0; count--) { \
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(val) = readl(addr); \
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if (cond) \
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break; \
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udelay(time_between_us); \
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} \
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(cond) ? 0 : -ETIMEDOUT; \
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})
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/**
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* readl_poll - Periodically poll an address until a condition is met
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* @addr: Address to poll
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* @val: Variable to read the value into
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* @cond: Break condition (usually involving @val)
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* @sleep_us: Maximum time to sleep between reads in uS (0 tight-loops)
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*
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* Must not be called from atomic context if sleep_us is used.
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*/
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#define readl_poll(addr, val, cond, sleep_us) \
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readl_poll_timeout(addr, val, cond, sleep_us, 0)
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/**
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* readl_tight_poll_timeout - Tight-loop on an address until a condition is met or a timeout occurs
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* @addr: Address to poll
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* @val: Variable to read the value into
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* @cond: Break condition (usually involving @val)
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* @timeout_us: Timeout in uS, 0 means never timeout
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*
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* Returns 0 on success and -ETIMEDOUT upon a timeout. In either
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* case, the last read value at @addr is stored in @val. Must not
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* be called from atomic context if timeout_us is used.
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*/
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#define readl_tight_poll_timeout(addr, val, cond, timeout_us) \
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readl_poll_timeout(addr, val, cond, 0, timeout_us)
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/**
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* readl_tight_poll - Tight-loop on an address until a condition is met
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* @addr: Address to poll
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* @val: Variable to read the value into
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* @cond: Break condition (usually involving @val)
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*
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* May be called from atomic context.
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*/
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#define readl_tight_poll(addr, val, cond) \
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readl_poll_timeout(addr, val, cond, 0, 0)
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#endif /* _LINUX_IOPOLL_H */
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