[PATCH 3/3] ARM: shmobile: timer: Fix preset_lpj leading to too short delays

[Simon Horman]

From: Geert Uytterhoeven <geert+rene...@glider.be>

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 11d4bb1bd067f9d0 ("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+rene...@glider.be>
Signed-off-by: Simon Horman <horms+rene...@verge.net.au>
---
 arch/arm/mach-shmobile/timer.c | 28 +++++++++++-----------------
 1 file changed, 11 insertions(+), 17 deletions(-)

diff --git a/arch/arm/mach-shmobile/timer.c b/arch/arm/mach-shmobile/timer.c
index ad008e4b0c49..67d79f9c6bad 100644
--- a/arch/arm/mach-shmobile/timer.c
+++ b/arch/arm/mach-shmobile/timer.c
@@ -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);
 }
-- 
2.7.0.rc3.207.g0ac5344