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authorRussell King <rmk+kernel@armlinux.org.uk>2018-12-13 14:02:48 +0000
committerRussell King <rmk+kernel@armlinux.org.uk>2019-02-01 22:05:23 +0000
commit6213f70e7c10fd4a01b65bad3826648fc78df8a8 (patch)
treec1296d53776c9668057f570485285754c2424ab5 /arch/arm/mach-exynos/platsmp.c
parent70678554c4c40f2cf8de5e7cd53fdd2c73387e51 (diff)
ARM: smp: remove arch-provided "pen_release"
Consolidating the "pen_release" stuff amongst the various SoC implementations gives credence to having a CPU holding pen for secondary CPUs. However, this is far from the truth. Many SoC implementations cargo-cult copied various bits of the pen release implementation from the initial Realview/Versatile Express implementation without understanding what it was or why it existed. The reason it existed is because these are _development_ platforms, and some board firmware is unable to individually control the startup of secondary CPUs. Moreover, they do not have a way to power down or reset secondary CPUs for hot-unplug. Hence, the pen_release implementation was designed for ARM Ltd's development platforms to provide a working implementation, even though it is very far from what is required. It was decided a while back to reduce the duplication by consolidating the "pen_release" variable, but this only made the situation worse - we have ended up with several implementations that read this variable but do not write it - again, showing the cargo-cult mentality at work, lack of proper review of new code, and in some cases a lack of testing. While it would be preferable to remove pen_release entirely from the kernel, this is not possible without help from the SoC maintainers, which seems to be lacking. However, I want to remove pen_release from arch code to remove the credence that having it gives. This patch removes pen_release from the arch code entirely, adding private per-SoC definitions for it instead, and explicitly stating that write_pen_release() is cargo-cult copied and should not be copied any further. Rename write_pen_release() in a similar fashion as well. Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Diffstat (limited to 'arch/arm/mach-exynos/platsmp.c')
-rw-r--r--arch/arm/mach-exynos/platsmp.c31
1 files changed, 18 insertions, 13 deletions
diff --git a/arch/arm/mach-exynos/platsmp.c b/arch/arm/mach-exynos/platsmp.c
index c39ffd2e2fe6..3795412c0189 100644
--- a/arch/arm/mach-exynos/platsmp.c
+++ b/arch/arm/mach-exynos/platsmp.c
@@ -28,6 +28,9 @@
extern void exynos4_secondary_startup(void);
+/* XXX exynos_pen_release is cargo culted code - DO NOT COPY XXX */
+volatile int exynos_pen_release = -1;
+
#ifdef CONFIG_HOTPLUG_CPU
static inline void cpu_leave_lowpower(u32 core_id)
{
@@ -57,7 +60,7 @@ static inline void platform_do_lowpower(unsigned int cpu, int *spurious)
wfi();
- if (pen_release == core_id) {
+ if (exynos_pen_release == core_id) {
/*
* OK, proper wakeup, we're done
*/
@@ -228,15 +231,17 @@ void exynos_core_restart(u32 core_id)
}
/*
- * Write pen_release in a way that is guaranteed to be visible to all
- * observers, irrespective of whether they're taking part in coherency
+ * XXX CARGO CULTED CODE - DO NOT COPY XXX
+ *
+ * Write exynos_pen_release in a way that is guaranteed to be visible to
+ * all observers, irrespective of whether they're taking part in coherency
* or not. This is necessary for the hotplug code to work reliably.
*/
-static void write_pen_release(int val)
+static void exynos_write_pen_release(int val)
{
- pen_release = val;
+ exynos_pen_release = val;
smp_wmb();
- sync_cache_w(&pen_release);
+ sync_cache_w(&exynos_pen_release);
}
static DEFINE_SPINLOCK(boot_lock);
@@ -247,7 +252,7 @@ static void exynos_secondary_init(unsigned int cpu)
* let the primary processor know we're out of the
* pen, then head off into the C entry point
*/
- write_pen_release(-1);
+ exynos_write_pen_release(-1);
/*
* Synchronise with the boot thread.
@@ -322,12 +327,12 @@ static int exynos_boot_secondary(unsigned int cpu, struct task_struct *idle)
/*
* The secondary processor is waiting to be released from
* the holding pen - release it, then wait for it to flag
- * that it has been released by resetting pen_release.
+ * that it has been released by resetting exynos_pen_release.
*
- * Note that "pen_release" is the hardware CPU core ID, whereas
+ * Note that "exynos_pen_release" is the hardware CPU core ID, whereas
* "cpu" is Linux's internal ID.
*/
- write_pen_release(core_id);
+ exynos_write_pen_release(core_id);
if (!exynos_cpu_power_state(core_id)) {
exynos_cpu_power_up(core_id);
@@ -376,13 +381,13 @@ static int exynos_boot_secondary(unsigned int cpu, struct task_struct *idle)
else
arch_send_wakeup_ipi_mask(cpumask_of(cpu));
- if (pen_release == -1)
+ if (exynos_pen_release == -1)
break;
udelay(10);
}
- if (pen_release != -1)
+ if (exynos_pen_release != -1)
ret = -ETIMEDOUT;
/*
@@ -392,7 +397,7 @@ static int exynos_boot_secondary(unsigned int cpu, struct task_struct *idle)
fail:
spin_unlock(&boot_lock);
- return pen_release != -1 ? ret : 0;
+ return exynos_pen_release != -1 ? ret : 0;
}
static void __init exynos_smp_prepare_cpus(unsigned int max_cpus)

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