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 emit a warning that the attempted power down will fail, to aid debugging system suspend where it is not currently obvious that a core has not really powered down and will block a full power down of the cluster. We use a ratelimited pr_warn since this path will also be hit by cpu idle if it attempts to put cores into the powered down state. Signed-off-by: Matt Redfearn <[email protected]> --- arch/mips/kernel/pm-cps.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/mips/kernel/pm-cps.c b/arch/mips/kernel/pm-cps.c index 421e06dfee72..45776613a5be 100644 --- a/arch/mips/kernel/pm-cps.c +++ b/arch/mips/kernel/pm-cps.c @@ -11,6 +11,7 @@ #include <linux/cpuhotplug.h> #include <linux/init.h> #include <linux/percpu.h> +#include <linux/ratelimit.h> #include <linux/slab.h> #include <asm/asm-offsets.h> @@ -143,6 +144,18 @@ int cps_pm_enter_state(enum cps_pm_state state) /* Setup the VPE to run mips_cps_pm_restore when started again */ if (IS_ENABLED(CONFIG_CPU_PM) && state == CPS_PM_POWER_GATED) { + unsigned int stat = read_cpc_cl_stat_conf(); + + if (stat & CPC_Cx_STAT_CONF_EJTAG_PROBE) { + /* + * If we're attempting to gate power to the core, the + * JTAG detect bit indicates that the CPC will instead + * put the core into clock-off state. Emit a warning. + */ + pr_warn_ratelimited("JTAG probe present - core%d will clock off instead of powering down\n", + core); + } + /* Power gating relies upon CPS SMP */ if (!mips_cps_smp_in_use()) return -EINVAL; -- 2.7.4
