From a9e0a1911b9a06ac7eff2eee9327defe5b899d54 Mon Sep 17 00:00:00 2001 From: Matt Redfearn Date: Tue, 20 Feb 2018 09:58:16 +0000 Subject: [PATCH] MIPS: pm-cps: Block system suspend when a JTAG probe is present 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 Signed-off-by: Matt Redfearn Cc: Ralf Baechle Cc: Paul Burton Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/18641/ Signed-off-by: James Hogan --- 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 421e06dfee728..55c3fbeb2df62 100644 --- a/arch/mips/kernel/pm-cps.c +++ b/arch/mips/kernel/pm-cps.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include @@ -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); } -- 2.39.5