powerpc/powernv: Re-enable imc trace-mode in kernel

commit <249fad73> ""powerpc/perf: Disable trace_imc pmu"
disables IMC(In-Memory Collection) trace-mode in kernel, since frequent
mode switching between accumulation mode and trace mode via the spr LDBAR
in the hardware can trigger a checkstop(system crash).

Patch to re-enable imc-trace mode in kernel.

The previous patch(1/2) in this series will address the mode switching issue
by implementing a global lock, and will restrict the usage of
accumulation and trace-mode at a time.
Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200313055238.8656-2-anju@linux.vnet.ibm.com

arch/powerpc/platforms/powernv/opal-imc.c

@@ -268,14 +268,7 @@ static int opal_imc_counters_probe(struct platform_device *pdev)
 			domain = IMC_DOMAIN_THREAD;
 			break;
 		case IMC_TYPE_TRACE:
-			/*
-			 * FIXME. Using trace_imc events to monitor application
-			 * or KVM thread performance can cause a checkstop
-			 * (system crash).
-			 * Disable it for now.
-			 */
-			pr_info_once("IMC: disabling trace_imc PMU\n");
-			domain = -1;
+			domain = IMC_DOMAIN_TRACE;
 			break;
 		default:
 			pr_warn("IMC Unknown Device type \n");