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ARM: shmobile: timer: Fix preset_lpj leading to too short delays

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On all shmobile ARM SoCs, loop-based delays may complete early, which
can be after only 1/3 (Cortex A9) or 1/2 (Cortex A7 or A15) of the
minimum required time.

This is caused by calculating preset_lpj based on incorrect assumptions
about the number of clock cycles per loop:
  - All of Cortex A7, A9, and A15 run __loop_delay() at 1 loop per
    CPU clock cycle,
  - As of commit 11d4bb1bd0 ("ARM: 7907/1: lib: delay-loop: Add
    align directive to fix BogoMIPS calculation"), Cortex A8 runs
    __loop_delay() at 1 loop per 2 instead of 3 CPU clock cycles.

On SoCs with Cortex A7 and/or A15 CPU cores, this went unnoticed, as
delays use the ARM arch timer if available. R-Car Gen2 doesn't work if
the arch timer is disabled. However, APE6 can be used without the arch
timer.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
This commit is contained in:
Geert Uytterhoeven 2016-01-11 19:41:12 +01:00 committed by Simon Horman
parent 01638a7f5e
commit c531fb27e9
1 changed files with 11 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
arch/arm/mach-shmobile/timer.c
View File

@ -40,8 +40,7 @@ static void __init shmobile_setup_delay_hz(unsigned int max_cpu_core_hz,
void __init shmobile_init_delay(void)
{
struct device_node *np, *cpus;
bool is_a7_a8_a9 = false;
bool is_a15 = false;
unsigned int div = 0;
bool has_arch_timer = false;
u32 max_freq = 0;
@ -55,27 +54,22 @@ void __init shmobile_init_delay(void)
if (!of_property_read_u32(np, "clock-frequency", &freq))
max_freq = max(max_freq, freq);
if (of_device_is_compatible(np, "arm,cortex-a8") ||
of_device_is_compatible(np, "arm,cortex-a9")) {
is_a7_a8_a9 = true;
} else if (of_device_is_compatible(np, "arm,cortex-a7")) {
is_a7_a8_a9 = true;
has_arch_timer = true;
} else if (of_device_is_compatible(np, "arm,cortex-a15")) {
is_a15 = true;
if (of_device_is_compatible(np, "arm,cortex-a8")) {
div = 2;
} else if (of_device_is_compatible(np, "arm,cortex-a9")) {
div = 1;
} else if (of_device_is_compatible(np, "arm,cortex-a7") ||
of_device_is_compatible(np, "arm,cortex-a15")) {
div = 1;
has_arch_timer = true;
}
}
of_node_put(cpus);
if (!max_freq)
if (!max_freq || !div)
return;
if (!has_arch_timer || !IS_ENABLED(CONFIG_ARM_ARCH_TIMER)) {
if (is_a7_a8_a9)
shmobile_setup_delay_hz(max_freq, 1, 3);
else if (is_a15)
shmobile_setup_delay_hz(max_freq, 2, 4);
}
if (!has_arch_timer || !IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
shmobile_setup_delay_hz(max_freq, 1, div);
}