From 6213f70e7c10fd4a01b65bad3826648fc78df8a8 Mon Sep 17 00:00:00 2001 From: Russell King Date: Thu, 13 Dec 2018 14:02:48 +0000 Subject: 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 --- arch/arm/mach-spear/generic.h | 2 ++ arch/arm/mach-spear/headsmp.S | 2 +- arch/arm/mach-spear/hotplug.c | 4 +++- arch/arm/mach-spear/platsmp.c | 27 ++++++++++++++++----------- 4 files changed, 22 insertions(+), 13 deletions(-) (limited to 'arch/arm/mach-spear') diff --git a/arch/arm/mach-spear/generic.h b/arch/arm/mach-spear/generic.h index 909b97c0b237..25b4c5e66e39 100644 --- a/arch/arm/mach-spear/generic.h +++ b/arch/arm/mach-spear/generic.h @@ -20,6 +20,8 @@ #include +extern volatile int spear_pen_release; + extern void spear13xx_timer_init(void); extern void spear3xx_timer_init(void); extern struct pl022_ssp_controller pl022_plat_data; diff --git a/arch/arm/mach-spear/headsmp.S b/arch/arm/mach-spear/headsmp.S index c52192dc3d9f..6e250b6c0aa2 100644 --- a/arch/arm/mach-spear/headsmp.S +++ b/arch/arm/mach-spear/headsmp.S @@ -43,5 +43,5 @@ pen: ldr r7, [r6] .align 1: .long . - .long pen_release + .long spear_pen_release ENDPROC(spear13xx_secondary_startup) diff --git a/arch/arm/mach-spear/hotplug.c b/arch/arm/mach-spear/hotplug.c index 12edd1cf8a12..0dd84f609627 100644 --- a/arch/arm/mach-spear/hotplug.c +++ b/arch/arm/mach-spear/hotplug.c @@ -16,6 +16,8 @@ #include #include +#include "generic.h" + static inline void cpu_enter_lowpower(void) { unsigned int v; @@ -57,7 +59,7 @@ static inline void spear13xx_do_lowpower(unsigned int cpu, int *spurious) for (;;) { wfi(); - if (pen_release == cpu) { + if (spear_pen_release == cpu) { /* * OK, proper wakeup, we're done */ diff --git a/arch/arm/mach-spear/platsmp.c b/arch/arm/mach-spear/platsmp.c index 39038a03836a..b1ff4bb86f6d 100644 --- a/arch/arm/mach-spear/platsmp.c +++ b/arch/arm/mach-spear/platsmp.c @@ -20,16 +20,21 @@ #include #include "generic.h" +/* XXX spear_pen_release is cargo culted code - DO NOT COPY XXX */ +volatile int spear_pen_release = -1; + /* - * 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 spear_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 spear_write_pen_release(int val) { - pen_release = val; + spear_pen_release = val; smp_wmb(); - sync_cache_w(&pen_release); + sync_cache_w(&spear_pen_release); } static DEFINE_SPINLOCK(boot_lock); @@ -42,7 +47,7 @@ static void spear13xx_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); + spear_write_pen_release(-1); /* * Synchronise with the boot thread. @@ -64,17 +69,17 @@ static int spear13xx_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 spear_pen_release. * - * Note that "pen_release" is the hardware CPU ID, whereas + * Note that "spear_pen_release" is the hardware CPU ID, whereas * "cpu" is Linux's internal ID. */ - write_pen_release(cpu); + spear_write_pen_release(cpu); timeout = jiffies + (1 * HZ); while (time_before(jiffies, timeout)) { smp_rmb(); - if (pen_release == -1) + if (spear_pen_release == -1) break; udelay(10); @@ -86,7 +91,7 @@ static int spear13xx_boot_secondary(unsigned int cpu, struct task_struct *idle) */ spin_unlock(&boot_lock); - return pen_release != -1 ? -ENOSYS : 0; + return spear_pen_release != -1 ? -ENOSYS : 0; } /* -- cgit v1.2.3