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Subject: Re: [PATCH 2/5] memstick: Prevent memstick host from getting runtime
 suspended during card detection
From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
In-Reply-To: <Pine.LNX.4.44L0.1807251353550.1467-100000@iolanthe.rowland.org>
Date:   Thu, 26 Jul 2018 15:01:56 +0800
Cc:     arnd@arndb.de, gregkh@linuxfoundation.org, ulf.hansson@linaro.org,
        bauer.chen@realtek.com, ricky_wu@realtek.com,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
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Message-Id: <10942DC1-3F18-4A87-A662-B8CD073FFA14@canonical.com>
References: <Pine.LNX.4.44L0.1807251353550.1467-100000@iolanthe.rowland.org>
To:     Alan Stern <stern@rowland.harvard.edu>
Sender: linux-kernel-owner@vger.kernel.org
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> On 2018Jul26, at 01:56, Alan Stern <stern@rowland.harvard.edu> wrote:
> 
> On Wed, 25 Jul 2018, Kai-Heng Feng wrote:
> 
>> 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@canonical.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..944fe0c93fa7 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_noidle(host->dev.parent);
>> 	dev_dbg(&host->dev, "memstick_check finished\n");
>> }
> 
> This should be pm_runtime_put(), not _put_noidle().  The reason is
> because if this call causes the PM runtime usage count to drop to 0,
> you do want the device to go into runtime suspend.

Will update in next version, thanks!

Kai-Heng

> 
> Alan Stern