If a JTAG probe is connected to a MIPS cluster, then the CPC detects it
and latches the CPC.STAT_CONF.EJTAG_PROBE bit to 1. While set,
attempting to send a power-down command to a core will be blocked, and
the CPC will instead send the core to clock-off state. This can
interfere with systems fully entering a low power state where all
cores, CM, GIC, etc are powered down.
Detect that a JTAG probe is / has been connected to the cluster and
block the suspend attempt.
Attempting to suspend the system while a JTAG probe is connected now
yields:
# echo mem > /sys/power/state
[ 11.654000] PM: Syncing filesystems ... done.
[ 11.658000] JTAG probe is connected - abort suspend
-sh: echo: write error: Operation not permitted
#
To restore suspend, the JTAG probe should be disconnected or put into
quiescent state. Platform code can then clear the
CPC.STAT_CONF.EJTAG_PROBE bit.
Reported-by: Ed Blake <ed.blake@xxxxxxxxxxx>
Signed-off-by: Matt Redfearn <matt.redfearn@xxxxxxxx>
series-cc: Ed Blake <ed.blake@xxxxxxxxxxx>
---
Changes in v3:
Remove #if defined(CONFIG_PM_SLEEP) around cps_pm_power_notifier which
results in build error if CONFIG_PM_SLEEP is not defined. I believed
that the pm_notifier() registration would harmlessly compile out if
!defined(CONFIG_PM_SLEEP). However, it actually casts the fn to void in
that case, resulting in a build error from the missing definition.
Changes in v2:
Fixed CPC_Cx_STAT_CONF_EJTAG_PROBE_MSK -> CPC_Cx_STAT_CONF_EJTAG_PROBE -
thanks kbuild test robot!
arch/mips/kernel/pm-cps.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/arch/mips/kernel/pm-cps.c b/arch/mips/kernel/pm-cps.c
index 421e06dfee72..55c3fbeb2df6 100644
--- a/arch/mips/kernel/pm-cps.c
+++ b/arch/mips/kernel/pm-cps.c
@@ -12,6 +12,7 @@
#include <linux/init.h>
#include <linux/percpu.h>
#include <linux/slab.h>
+#include <linux/suspend.h>
#include <asm/asm-offsets.h>
#include <asm/cacheflush.h>
@@ -670,6 +671,34 @@ static int cps_pm_online_cpu(unsigned int cpu)
return 0;
}
+static int cps_pm_power_notifier(struct notifier_block *this,
+ unsigned long event, void *ptr)
+{
+ unsigned int stat;
+
+ switch (event) {
+ case PM_SUSPEND_PREPARE:
+ stat = read_cpc_cl_stat_conf();
+ /*
+ * If we're attempting to suspend the system and power down all
+ * of the cores, the JTAG detect bit indicates that the CPC will
+ * instead put the cores into clock-off state. In this state
+ * a connected debugger can cause the CPU to attempt
+ * interactions with the powered down system. At best this will
+ * fail. At worst, it can hang the NoC, requiring a hard reset.
+ * To avoid this, just block system suspend if a JTAG probe
+ * is detected.
+ */
+ if (stat & CPC_Cx_STAT_CONF_EJTAG_PROBE) {
+ pr_warn("JTAG probe is connected - abort suspend\n");
+ return NOTIFY_BAD;
+ }
+ return NOTIFY_DONE;
+ default:
+ return NOTIFY_DONE;
+ }
+}
+
static int __init cps_pm_init(void)
{
/* A CM is required for all non-coherent states */
@@ -705,6 +734,8 @@ static int __init cps_pm_init(void)
pr_warn("pm-cps: no CPC, clock & power gating unavailable\n");
}
+ pm_notifier(cps_pm_power_notifier, 0);
+
return cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mips/cps_pm:online",
cps_pm_online_cpu, NULL);
}
--
2.7.4
