From: Finley Xiao <finley.xiao@rock-chips.com>
Date: Mon, 15 May 2017 01:42:29 +0000 (+0800)
Subject: PM / devfreq: Lock CPU online/offline in rockchip_dmcfreq_target()
X-Git-Tag: release-20171130_firefly~4^2~559
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=08e0c3fbe7cda3e0601ea730b102874e05114823;p=firefly-linux-kernel-4.4.55.git

PM / devfreq: Lock CPU online/offline in rockchip_dmcfreq_target()

To protect against races with concurrent CPU online/offline, call
get_online_cpus() before change frequency.

Change-Id: I5b97cd7eff6a1c4828ab30bc165fb2aa8b460bb3
Signed-off-by: Finley Xiao <finley.xiao@rock-chips.com>
---

diff --git a/drivers/devfreq/rockchip_dmc.c b/drivers/devfreq/rockchip_dmc.c
index 4cf6a1999248..81a2f2c89897 100644
--- a/drivers/devfreq/rockchip_dmc.c
+++ b/drivers/devfreq/rockchip_dmc.c
@@ -17,6 +17,7 @@
 #include <drm/drmP.h>
 #include <linux/arm-smccc.h>
 #include <linux/clk.h>
+#include <linux/cpu.h>
 #include <linux/delay.h>
 #include <linux/devfreq.h>
 #include <linux/devfreq-event.h>
@@ -217,7 +218,16 @@ static int rockchip_dmcfreq_target(struct device *dev, unsigned long *freq,
 		}
 	}
 
+	/*
+	 * We need to prevent cpu hotplug from happening while a dmc freq rate
+	 * change is happening.
+	 */
+	get_online_cpus();
+
 	err = clk_set_rate(dmcfreq->dmc_clk, target_rate);
+
+	put_online_cpus();
+
 	if (err) {
 		dev_err(dev, "Cannot set frequency %lu (%d)\n",
 			target_rate, err);