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MIPS: pm-cps: Block system suspend when a JTAG probe is present

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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@sondrel.com>
Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18641/
Signed-off-by: James Hogan <jhogan@kernel.org>
This commit is contained in:
Matt Redfearn 2018-02-20 09:58:16 +00:00 committed by James Hogan
parent ce6828faeb
commit b2ed33a895
No known key found for this signature in database
GPG Key ID: 6C0B6993DE38767A
1 changed files with 31 additions and 0 deletions
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31
arch/mips/kernel/pm-cps.c
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@ -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);
}