[PATCH] perf/x86/intel/uncore: fix IMC missing box initialization

[Stephane Eranian <eranian@google.com>]

This patch fixes a bug introduced by:

commit c05199e5a57a579fea1e8fa65e2b511ceb524ffc
Author: Kan Liang <kan.liang@intel.com>
Date:   Tue Jan 20 04:54:25 2015 +0000

    perf/x86/intel/uncore: Move uncore_box_init() out of driver initialization

It moves uncore_box_init() out of place but this meant that for desktop memory
controller (IMC) PCI-based PMU, the intialization was now missing causing a
crash at first access. This patch fixes the issue by adding the call to the
uncore_enable_box() in snb_uncore_imc_read_counter() to ensure the box
is initialized and the PCI BAR is io-remapped.

Signed-off-by: Stephane Eranian <eranian@google.com>
--

diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore_snb.c b/arch/x86/kernel/cpu/perf_event_intel_uncore_snb.c
index 4562e9e..755ec05 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_uncore_snb.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_uncore_snb.c
@@ -329,6 +329,9 @@ static void snb_uncore_imc_event_start(struct perf_event *event, int flags)
 
 	list_add_tail(&event->active_entry, &box->active_list);
 
+	if (box->n_active == 1)
+		uncore_enable_box(box);
+
 	count = snb_uncore_imc_read_counter(box, event);
 	local64_set(&event->hw.prev_count, count);