Re: [PATCH v4 5/5] arm: exynos: Add MCPM call-back functions

Hi Nicolas,

On Fri, May 2, 2014 at 11:46 PM, Nicolas Pitre [off-list ref] wrote:

On Fri, 2 May 2014, Abhilash Kesavan wrote:

quoted

Add machine-dependent MCPM call-backs for Exynos5420. These are used
to power up/down the secondary CPUs during boot, shutdown, s2r and
switching.

Signed-off-by: Thomas Abraham <redacted>
Signed-off-by: Inderpal Singh <redacted>
Signed-off-by: Andrew Bresticker <redacted>
Signed-off-by: Abhilash Kesavan <redacted>

OK.... There is still a detail wrong.  At least we are converging.

quoted

---
 arch/arm/mach-exynos/Kconfig       |    8 +
 arch/arm/mach-exynos/Makefile      |    2 +
 arch/arm/mach-exynos/mcpm-exynos.c |  345 ++++++++++++++++++++++++++++++++++++
 arch/arm/mach-exynos/regs-pmu.h    |    3 +
 4 files changed, 358 insertions(+)
 create mode 100644 arch/arm/mach-exynos/mcpm-exynos.c

diff --git a/arch/arm/mach-exynos/Kconfig b/arch/arm/mach-exynos/Kconfig
index 5c34dc2..138070e 100644
--- a/arch/arm/mach-exynos/Kconfig
+++ b/arch/arm/mach-exynos/Kconfig

@@ -73,4 +73,12 @@ config SOC_EXYNOS5440

 endmenu

+config EXYNOS5420_MCPM
+     bool "Exynos5420 Multi-Cluster PM support"
+     depends on MCPM && SOC_EXYNOS5420
+     select ARM_CCI
+     help
+       This is needed to provide CPU and cluster power management
+       on Exynos5420 implementing big.LITTLE.
+
 endif

diff --git a/arch/arm/mach-exynos/Makefile b/arch/arm/mach-exynos/Makefile
index a656dbe..01bc9b9 100644
--- a/arch/arm/mach-exynos/Makefile
+++ b/arch/arm/mach-exynos/Makefile

@@ -29,3 +29,5 @@ obj-$(CONFIG_ARCH_EXYNOS)   += firmware.o

 plus_sec := $(call as-instr,.arch_extension sec,+sec)
 AFLAGS_exynos-smc.o          :=-Wa,-march=armv7-a$(plus_sec)
+
+obj-$(CONFIG_EXYNOS5420_MCPM)        += mcpm-exynos.o

diff --git a/arch/arm/mach-exynos/mcpm-exynos.c b/arch/arm/mach-exynos/mcpm-exynos.c
new file mode 100644
index 0000000..d0f7461
--- /dev/null
+++ b/arch/arm/mach-exynos/mcpm-exynos.c

@@ -0,0 +1,345 @@
+/*
+ * Copyright (c) 2014 Samsung Electronics Co., Ltd.
+ *           http://www.samsung.com
+ *
+ * arch/arm/mach-exynos/mcpm-exynos.c
+ *
+ * Based on arch/arm/mach-vexpress/dcscb.c
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/arm-cci.h>
+#include <linux/delay.h>
+#include <linux/io.h>
+#include <linux/of_address.h>
+
+#include <asm/cputype.h>
+#include <asm/cp15.h>
+#include <asm/mcpm.h>
+
+#include "regs-pmu.h"
+#include "common.h"
+
+#define EXYNOS5420_CPUS_PER_CLUSTER  4
+#define EXYNOS5420_NR_CLUSTERS               2
+
+/* Non-secure iRAM base address */
+static void __iomem *ns_sram_base_addr;
+
+/*
+ * The common v7_exit_coherency_flush API could not be used because of the
+ * Erratum 799270 workaround. This macro is the same as the common one (in
+ * arch/arm/include/asm/cacheflush.h) except for the erratum handling.
+ */
+#define exynos_v7_exit_coherency_flush(level) \
+     asm volatile( \
+     "stmfd  sp!, {fp, ip}\n\t"\
+     "mrc    p15, 0, r0, c1, c0, 0   @ get SCTLR\n\t" \
+     "bic    r0, r0, #"__stringify(CR_C)"\n\t" \
+     "mcr    p15, 0, r0, c1, c0, 0   @ set SCTLR\n\t" \
+     "isb\n\t"\
+     "bl     v7_flush_dcache_"__stringify(level)"\n\t" \
+     "clrex\n\t"\
+     "mrc    p15, 0, r0, c1, c0, 1   @ get ACTLR\n\t" \
+     "bic    r0, r0, #(1 << 6)       @ disable local coherency\n\t" \
+     /* Dummy Load of a device register to avoid Erratum 799270 */ \
+     "ldr    r4, [%0]\n\t" \
+     "and    r4, r4, #0\n\t" \
+     "orr    r0, r0, r4\n\t" \
+     "mcr    p15, 0, r0, c1, c0, 1   @ set ACTLR\n\t" \
+     "isb\n\t" \
+     "dsb\n\t" \
+     "ldmfd  sp!, {fp, ip}" \
+     : \
+     : "Ir" (S5P_INFORM0) \
+     : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", \
+       "r9", "r10", "lr", "memory")
+
+/*
+ * We can't use regular spinlocks. In the switcher case, it is possible
+ * for an outbound CPU to call power_down() after its inbound counterpart
+ * is already live using the same logical CPU number which trips lockdep
+ * debugging.
+ */
+static arch_spinlock_t exynos_mcpm_lock = __ARCH_SPIN_LOCK_UNLOCKED;
+static int
+cpu_use_count[EXYNOS5420_CPUS_PER_CLUSTER][EXYNOS5420_NR_CLUSTERS];
+
+#define exynos_cluster_unused(cluster) \
+     (!cpu_use_count[0][cluster] && \
+      !cpu_use_count[1][cluster] && \
+      !cpu_use_count[2][cluster] && \
+      !cpu_use_count[3][cluster])
+
+static int exynos_cluster_power_control(unsigned int cluster, int enable)
+{
+     unsigned int tries = 100;
+     unsigned int val;
+
+     if (enable) {
+             exynos_cluster_powerup(cluster);
+             val = S5P_CORE_LOCAL_PWR_EN;
+     } else {
+             exynos_cluster_powerdown(cluster);
+             val = 0;
+     }
+
+     /* Wait until cluster power control is applied */
+     while (tries--) {
+             if (exynos_cluster_power_state(cluster) == val)
+                     return 0;
+
+             cpu_relax();
+     }
+     pr_warn("timed out waiting for cluster %u to power %s\n", cluster,
+             enable ? "on" : "off");
+
+     return -ETIMEDOUT;
+}
+
+static int exynos_power_up(unsigned int cpu, unsigned int cluster)
+{
+     unsigned int cpunr = cpu + (cluster * EXYNOS5420_CPUS_PER_CLUSTER);
+     int err = 0;
+
+     pr_debug("%s: cpu %u cluster %u\n", __func__, cpu, cluster);
+     if (cpu >= EXYNOS5420_CPUS_PER_CLUSTER ||
+             cluster >= EXYNOS5420_NR_CLUSTERS)
+             return -EINVAL;
+
+     /*
+      * Since this is called with IRQs enabled, and no arch_spin_lock_irq
+      * variant exists, we need to disable IRQs manually here.
+      */
+     local_irq_disable();
+     arch_spin_lock(&exynos_mcpm_lock);
+
+     cpu_use_count[cpu][cluster]++;
+     if (cpu_use_count[cpu][cluster] == 1) {
+             bool was_cluster_down =
+                     __mcpm_cluster_state(cluster) == CLUSTER_DOWN;

This is racy.  I probably made this comment already.  The MCPM cluster
state may change in mcpm-head.S where concurrency protection is achieved
with a different mechanism.

What you should do instead is to redefine exynos_cluster_unused() into
exynos_cluster_usecnt() and simply add all counts together.  You could
even have:

#define exynos_cluster_unused(cluster) !exynos_cluster_usecnt(cluster)

Yet, here you should use:

        bool was_cluster_down = (exynos_cluster_usecnt(cluster) == 1);

Fixed as per suggestion.

quoted

+
+             /*
+              * Turn on the cluster (L2/COMMON) and then power on the
+              * cores.
+              */
+             if (was_cluster_down)
+                     err = exynos_cluster_power_control(cluster, 1);
+
+             if (!err)
+                     exynos_cpu_powerup(cpunr);
+             else
+                     exynos_cluster_power_control(cluster, 0);
+     } else if (cpu_use_count[cpu][cluster] != 2) {
+             /*
+              * The only possible values are:
+              * 0 = CPU down
+              * 1 = CPU (still) up
+              * 2 = CPU requested to be up before it had a chance
+              *     to actually make itself down.
+              * Any other value is a bug.
+              */
+             BUG();
+     }
+
+     arch_spin_unlock(&exynos_mcpm_lock);
+     local_irq_enable();
+
+     return err;
+}
+
+static void exynos_power_down(void)
+{
+     unsigned int mpidr, cpu, cluster;
+     bool last_man = false, skip_wfi = false;
+     unsigned int cpunr;
+
+     mpidr = read_cpuid_mpidr();
+     cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);
+     cluster = MPIDR_AFFINITY_LEVEL(mpidr, 1);
+     cpunr =  cpu + (cluster * EXYNOS5420_CPUS_PER_CLUSTER);
+
+     pr_debug("%s: cpu %u cluster %u\n", __func__, cpu, cluster);
+     BUG_ON(cpu >= EXYNOS5420_CPUS_PER_CLUSTER ||
+                     cluster >= EXYNOS5420_NR_CLUSTERS);
+
+     __mcpm_cpu_going_down(cpu, cluster);
+
+     arch_spin_lock(&exynos_mcpm_lock);
+     BUG_ON(__mcpm_cluster_state(cluster) != CLUSTER_UP);
+     cpu_use_count[cpu][cluster]--;
+     if (cpu_use_count[cpu][cluster] == 0) {
+             exynos_cpu_powerdown(cpunr);
+
+             if (exynos_cluster_unused(cluster))
+                     last_man = true;
+     } else if (cpu_use_count[cpu][cluster] == 1) {
+             /*
+              * A power_up request went ahead of us.
+              * Even if we do not want to shut this CPU down,
+              * the caller expects a certain state as if the WFI
+              * was aborted.  So let's continue with cache cleaning.
+              */
+             skip_wfi = true;
+     } else {
+             BUG();
+     }
+
+     /*
+      * TODO: Turn off the clusters when all cores in the cluster
+      * are down to achieve significant power savings.
+      */

This comment should actually be located right after the
"if (exynos_cluster_unused(cluster))" above.  That is where the cluster
control should be applied, assuming it'll be effective only when WFI is
executed.

OK.

quoted

+     if (last_man && __mcpm_outbound_enter_critical(cpu, cluster)) {
+             arch_spin_unlock(&exynos_mcpm_lock);
+
+             /* Flush all cache levels for this cluster. */
+             exynos_v7_exit_coherency_flush(all);
+
+             /*
+              * Disable cluster-level coherency by masking
+              * incoming snoops and DVM messages:
+              */
+             cci_disable_port_by_cpu(mpidr);
+
+             __mcpm_outbound_leave_critical(cluster, CLUSTER_DOWN);
+     } else {
+             arch_spin_unlock(&exynos_mcpm_lock);
+
+             if (read_cpuid_part_number() == ARM_CPU_PART_CORTEX_A15) {
+                     /*
+                      * On the Cortex-A15 we need to disable
+                      * L2 prefetching before flushing the cache.
+                      */
+                     asm volatile(
+                     "mcr    p15, 1, %0, c15, c0, 3\n\t"
+                     "isb\n\t"
+                     "dsb"
+                     : : "r" (0x400));
+             }

This doesn't belong here.  That is for the last_man only to do, right
before the "Flush all cache levels for this cluster" comment.

This was a bad miss on my part. Will fix.

The rest looks fine to me.

Will post v5 soon.

Regards,
Abhilash

Nicolas

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