u-boot/arch/arm/cpu/armv8/generic_timer.c
Andre Przywara be0d217952 arm: timer: sunxi: add Allwinner timer erratum workaround
The Allwinner A64 SoCs suffers from an arch timer implementation erratum,
where sometimes the lower 11 bits of the counter value erroneously
become all 0's or all 1's [1]. This leads to sudden jumps, both forwards and
backwards, with the latter one often showing weird behaviour.
Port the workaround proposed for Linux to U-Boot and activate it for all
A64 boards.
This fixes crashes when accessing MMC devices (SD cards), caused by a
recent change to actually use the counter value for timeout checks.

Fixes: 5ff8e54888 ("sunxi: improve throughput
in the sunxi_mmc driver")

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-May/576886.html

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Andreas Färber <afaerber@suse.de>
Tested-by: Guillaume Gardet <guillaume.gardet@free.fr>
2018-07-03 22:00:00 +05:30

113 lines
2.8 KiB
C

// SPDX-License-Identifier: GPL-2.0+
/*
* (C) Copyright 2013
* David Feng <fenghua@phytium.com.cn>
*/
#include <common.h>
#include <command.h>
#include <asm/system.h>
DECLARE_GLOBAL_DATA_PTR;
/*
* Generic timer implementation of get_tbclk()
*/
unsigned long get_tbclk(void)
{
unsigned long cntfrq;
asm volatile("mrs %0, cntfrq_el0" : "=r" (cntfrq));
return cntfrq;
}
#ifdef CONFIG_SYS_FSL_ERRATUM_A008585
/*
* FSL erratum A-008585 says that the ARM generic timer counter "has the
* potential to contain an erroneous value for a small number of core
* clock cycles every time the timer value changes".
* This sometimes leads to a consecutive counter read returning a lower
* value than the previous one, thus reporting the time to go backwards.
* The workaround is to read the counter twice and only return when the value
* was the same in both reads.
* Assumes that the CPU runs in much higher frequency than the timer.
*/
unsigned long timer_read_counter(void)
{
unsigned long cntpct;
unsigned long temp;
isb();
asm volatile("mrs %0, cntpct_el0" : "=r" (cntpct));
asm volatile("mrs %0, cntpct_el0" : "=r" (temp));
while (temp != cntpct) {
asm volatile("mrs %0, cntpct_el0" : "=r" (cntpct));
asm volatile("mrs %0, cntpct_el0" : "=r" (temp));
}
return cntpct;
}
#elif CONFIG_SUNXI_A64_TIMER_ERRATUM
/*
* This erratum sometimes flips the lower 11 bits of the counter value
* to all 0's or all 1's, leading to jumps forwards or backwards.
* Backwards jumps might be interpreted all roll-overs and be treated as
* huge jumps forward.
* The workaround is to check whether the lower 11 bits of the counter are
* all 0 or all 1, then discard this value and read again.
* This occasionally discards valid values, but will catch all erroneous
* reads and fixes the problem reliably. Also this mostly requires only a
* single read, so does not have any significant overhead.
* The algorithm was conceived by Samuel Holland.
*/
unsigned long timer_read_counter(void)
{
unsigned long cntpct;
isb();
do {
asm volatile("mrs %0, cntpct_el0" : "=r" (cntpct));
} while (((cntpct + 1) & GENMASK(10, 0)) <= 1);
return cntpct;
}
#else
/*
* timer_read_counter() using the Arm Generic Timer (aka arch timer).
*/
unsigned long timer_read_counter(void)
{
unsigned long cntpct;
isb();
asm volatile("mrs %0, cntpct_el0" : "=r" (cntpct));
return cntpct;
}
#endif
uint64_t get_ticks(void)
{
unsigned long ticks = timer_read_counter();
gd->arch.tbl = ticks;
return ticks;
}
unsigned long usec2ticks(unsigned long usec)
{
ulong ticks;
if (usec < 1000)
ticks = ((usec * (get_tbclk()/1000)) + 500) / 1000;
else
ticks = ((usec / 10) * (get_tbclk() / 100000));
return ticks;
}
ulong timer_get_boot_us(void)
{
u64 val = get_ticks() * 1000000;
return val / get_tbclk();
}