linux-kernel - Re: [PATCH] USB: core: Add warm reset while reset-resuming SuperSpeed HUBs

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Date:	Tue, 10 Dec 2013 11:00:25 +0530
From:	Vikas Sajjan <sajjan.linux@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Vikas Sajjan <vikas.sajjan@...aro.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	vpalatin@...omium.org, jwerner@...omium.org, tianyu.lan@...el.com,
	burzalodowa@...il.com, gregkh@...uxfoundation.org,
	gautam.vivek@...sung.com, Douglas Anderson <dianders@...omium.org>,
	balbi@...com, sunil joshi <joshi@...sung.com>
Subject: Re: [PATCH] USB: core: Add warm reset while reset-resuming SuperSpeed HUBs

Hi Alan,

On Mon, Dec 9, 2013 at 8:54 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Mon, 9 Dec 2013, Vikas Sajjan wrote:
>
>> Does warm reset while activating SuperSpeed HUBs if the hub activate type
>> is HUB_RESET_RESUME.
>>
>> When we do Suspend-to-RAM with (any one of the 16, 32, 64 Jetflash) transcend
>> USB 3.0 device connected on 3.0 port, during resume I noticed that the
>> XHCI controller has moved to sometimes RECOVERY, POLLING or INACTIVE STATE.
>> This behaviour is inconsistent and the connection with connected USB 3.0 device
>> on 3.0 port was LOST.
>>
>> Doing warm reset while activating SuperSpeed HUBs if the hub
>> activate type is HUB_RESET_RESUME, gets the connected device to the stable state.
>>
>> Reviewed at https://chromium-review.googlesource.com/#/c/177132/
>>
>> Tested on exynos5420 and exynos5250 with Transcend Jetflash USB 3.0 device (8564:1000)
>>
>> rebased on Greg Kroah-Hartman's usb-next
>> git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
>>
>> Signed-off-by: Vikas Sajjan <vikas.sajjan@...sung.com>
>> ---
>>  drivers/usb/core/hub.c |   41 +++++++++++++++++++++++++----------------
>>  1 file changed, 25 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
>> index a7c04e2..d8432b0 100644
>> --- a/drivers/usb/core/hub.c
>> +++ b/drivers/usb/core/hub.c
>
>> @@ -1093,6 +1108,16 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
>>               u16 portstatus, portchange;
>>
>>               portstatus = portchange = 0;
>> +
>> +             /* Some connected devices might be still in unknown state even
>> +              * after reset-resume, a WARM_RESET gets the connected device
>> +              * to the normal state.
>> +              */
>> +             if (udev && hub_is_superspeed(hub->hdev) &&
>> +                                             type == HUB_RESET_RESUME)
>> +                     hub_port_reset(hub, port1, NULL,
>> +                                             HUB_BH_RESET_TIME, true);
>
> Please don't do this all the time to every attached port.  Do it only
> when it is really needed.
>
> Shouldn't you pass udev as the third argument?  If not, please explain
> why not.

yea, I have NOT tried passing udev as the third argument.


>
> Finally, I don't see why you put this in hub_activate().  Isn't it more
> closely connected with the reset-resume procedure for the child device?


I was trying to add a FIX in usb_port_resume(), but in our case we
have CONFIG_USB_DEFAULT_PERSIST disabled.

Interestingly, if I disable the CONFIG_USB_DEFAULT_PERSIST, then the
function usb_port_resume() will never be called and transcend Jetflash
device Suspend-to-RAM fails.

In normal scenario (ie., CONFIG_USB_DEFAULT_PERSIST=y) the sequence is:
===========================================================================
Step 1: For Root HUB :
usb_resume_both() ---> usb_resume_device() -> generic_resume() -->
hcd_bus_resume() --> xhci_bus_resume().
                              |
                              |-->usb_resume_interface() --->
hub_reset_resume() -->  xhci_update_hub_device()

Step 2:  For the Device connected
usb_resume_both() ---> usb_resume_device() ->
generic_resume()-->usb_port_resume()-->hub_port_logical_disconnect()
--> hub_port_disable() --> hub_usb3_port_disable().


In our scenario (ie., CONFIG_USB_DEFAULT_PERSIST=N) the sequence is:
===============================================================================
Step 1: For Root HUB
usb_resume_both() ---> usb_resume_device() -> generic_resume() -->
hcd_bus_resume() --> xhci_bus_resume().
                              |
                              |-->usb_resume_interface() --->
hub_reset_resume() -->  xhci_update_hub_device()

Step 2 :  Never occurs

So Suspend-to-RAM fails.

Hence i added a FIX in  hub_reset_resume().

Let me know if I am wrong.

>
> Alan Stern
>
> --
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