linux-kernel - Re: [PATCH 4/5] memstick: rtsx_usb_ms: Support runtime power management

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Date:   Fri, 24 Aug 2018 08:28:06 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        "Bauer.Chen" <bauer.chen@...ltek.com>, ricky_wu@...ltek.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 4/5] memstick: rtsx_usb_ms: Support runtime power management

On 23 August 2018 at 10:03, Kai-Heng Feng <kai.heng.feng@...onical.com> wrote:
> Hi Ulf,
>
> Sorry for the late reply.
>
>
> at 21:14, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
>> On 31 July 2018 at 08:17, Kai-Heng Feng <kai.heng.feng@...onical.com>
>> wrote:
>>>
>>> In order to let host's parent device, rtsx_usb, to use USB remote wake
>>> up signaling to do card detection, it needs to be suspended. Hence it's
>>> necessary to add runtime PM support for the memstick host.
>>>
>>> To keep memstick host stays suspended when it's not in use, convert the
>>> card detection function from kthread to delayed_work, which can be
>>> scheduled when the host is resumed and can be canceled when the host is
>>> suspended.
>>>
>>> Use an idle function check if there's no card and the power mode is
>>> MEMSTICK_POWER_OFF. If both criteria are met, put the device to suspend.
>>>
>>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
>>> ---
>>>  drivers/memstick/host/rtsx_usb_ms.c | 138 ++++++++++++++--------------
>>>  1 file changed, 71 insertions(+), 67 deletions(-)
>>>
>>> diff --git a/drivers/memstick/host/rtsx_usb_ms.c
>>> b/drivers/memstick/host/rtsx_usb_ms.c
>>> index cd12f3d1c088..126eb310980a 100644
>>> --- a/drivers/memstick/host/rtsx_usb_ms.c
>>> +++ b/drivers/memstick/host/rtsx_usb_ms.c
>>> @@ -40,15 +40,14 @@ struct rtsx_usb_ms {
>>>
>>>         struct mutex            host_mutex;
>>>         struct work_struct      handle_req;
>>> -
>>> -       struct task_struct      *detect_ms;
>>> -       struct completion       detect_ms_exit;
>>> +       struct delayed_work     poll_card;
>>>
>>>         u8                      ssc_depth;
>>>         unsigned int            clock;
>>>         int                     power_mode;
>>>         unsigned char           ifmode;
>>>         bool                    eject;
>>> +       bool                    suspend;
>>>  };
>>>
>>>  static inline struct device *ms_dev(struct rtsx_usb_ms *host)
>>> @@ -524,7 +523,7 @@ static void rtsx_usb_ms_handle_req(struct work_struct
>>> *work)
>>>         int rc;
>>>
>>>         if (!host->req) {
>>> -               pm_runtime_get_sync(ms_dev(host));
>>> +               pm_runtime_get_noresume(ms_dev(host));
>>
>>
>> I don't think this is safe.
>>
>> The memstick core doesn't manage runtime PM, hence there are no
>> guarantee that the device is runtime resumed at this point, or is
>> there?
>
>
> No guarantees there.
> Right now this only gets call when the host is powered on.
>
>>
>>>                do {
>>>                         rc = memstick_next_req(msh, &host->req);
>>>                         dev_dbg(ms_dev(host), "next req %d\n", rc);
>>> @@ -545,7 +544,7 @@ static void rtsx_usb_ms_handle_req(struct work_struct
>>> *work)
>>>                                                 host->req->error);
>>>                         }
>>>                 } while (!rc);
>>> -               pm_runtime_put(ms_dev(host));
>>> +               pm_runtime_put_noidle(ms_dev(host));
>>
>>
>> According to the above, I think this should stay as is. Or perhaps you
>> want to use pm_runtime_put_sync() instead, as to avoid the device from
>> being unnecessary resumed and hence also its parent.
>
>
> The tricky part is that pm_runtime_put_sync() calls rtsx_usb_ms_set_param()
> which calls pm_runtime_* helpers again

Why does a pm_runtime_put_sync() triggers a call to
rtsx_usb_ms_set_param()? It should not.

Ahh, that's because you have implemented the ->runtime_suspend()
callback to wrongly call memstick_suspend_host(). Drop that change,
then you should be able to call pm_runtime_put_sync() here and at
other places correctly.

>
> So maybe add runtime PM support to memstick core is the only way to support
> it properly?
>

It shouldn't be needed, and I wonder about if the effort is worth it,
especially since it seems that the only memstick driver that using
runtime PM is rtsx_usb_ms.

BTW, are you testing this change by using a memstick card, since I
haven't seen them for ages. :-)

[...]

Kind regards
Uffe