linux-kernel - [PATCH 2/5] memstick: Prevent memstick host from getting runtime suspended during card detection

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Message-Id: <20180731061721.15831-3-kai.heng.feng@canonical.com>
Date:   Tue, 31 Jul 2018 14:17:18 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     arnd@...db.de, gregkh@...uxfoundation.org
Cc:     ulf.hansson@...aro.org, stern@...land.harvard.edu,
        bauer.chen@...ltek.com, ricky_wu@...ltek.com,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Kai-Heng Feng <kai.heng.feng@...onical.com>
Subject: [PATCH 2/5] memstick: Prevent memstick host from getting runtime suspended during card detection

We can use MEMSTICK_POWER_{ON,OFF} along with pm_runtime_{get,put}
helpers to let memstick host support runtime pm.

There's a small window between memstick_detect_change() and its queued
work, memstick_check(). In this window the rpm count may go down to zero
before the memstick host powers on, so the host can be inadvertently
suspended.

Increment rpm count before calling memstick_check(), and decrement rpm
count afterward, as now we are sure the memstick host should be
suspended or not.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
---
 drivers/memstick/core/memstick.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/memstick/core/memstick.c b/drivers/memstick/core/memstick.c
index 76382c858c35..5f16a8826401 100644
--- a/drivers/memstick/core/memstick.c
+++ b/drivers/memstick/core/memstick.c
@@ -18,6 +18,7 @@
 #include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/module.h>
+#include <linux/pm_runtime.h>
 
 #define DRIVER_NAME "memstick"
 
@@ -209,6 +210,7 @@ static int memstick_dummy_check(struct memstick_dev *card)
  */
 void memstick_detect_change(struct memstick_host *host)
 {
+	pm_runtime_get_noresume(host->dev.parent);
 	queue_work(workqueue, &host->media_checker);
 }
 EXPORT_SYMBOL(memstick_detect_change);
@@ -479,6 +481,8 @@ static void memstick_check(struct work_struct *work)
 		host->set_param(host, MEMSTICK_POWER, MEMSTICK_POWER_OFF);
 
 	mutex_unlock(&host->lock);
+
+	pm_runtime_put(host->dev.parent);
 	dev_dbg(&host->dev, "memstick_check finished\n");
 }
 
-- 
2.17.1