linux-kernel - Re: [PATCH] usb: musb: Force-disable pullup on shutdown

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Message-Id: <1554305491.1177.0@crapouillou.net>
Date:   Wed, 03 Apr 2019 17:31:31 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Bin Liu <b-liu@...com>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, od@...c.me
Subject: Re: [PATCH] usb: musb: Force-disable pullup on shutdown



Le mer. 3 avril 2019 à 15:26, Bin Liu <b-liu@...com> a écrit :
> On Tue, Apr 02, 2019 at 09:58:42PM +0200, Paul Cercueil wrote:
>>  Hi,
>> 
>>  Le lun. 1 avril 2019 à 20:20, Bin Liu <b-liu@...com> a écrit :
>>  >On Mon, Apr 01, 2019 at 07:46:22PM +0200, Paul Cercueil wrote:
>>  >>
>>  >>
>>  >> Le lun. 1 avril 2019 à 19:17, Bin Liu <b-liu@...com> a écrit :
>>  >> >On Thu, Mar 21, 2019 at 03:42:46PM +0100, Paul Cercueil wrote:
>>  >> >> When the musb is shutdown, for instance when the driver is
>>  >>unloaded,
>>  >> >> force-disable the pullup. Otherwise, the host will still see
>>  >> >>the gadget
>>  >> >> device even after the shutdown.
>>  >> >
>>  >> >how would this happen?
>>  >> >
>>  >> >when musb-hdrc driver is unloaded, udc core removes the bound
>>  >>gadget
>>  >> >driver which calls musb_gadget_pullup() to disable the pullup.
>>  >>
>>  >> I'm testing with the jz4740-musb driver. I don't unload the
>>  >>module (it's
>>  >> built-in) but unbind it from sysfs.
>>  >
>>  >I did unbind too.
>>  >
>>  >root@...35x-evm:/sys/bus/platform/drivers/musb-hdrc# echo
>>  >musb-hdrc.0 > unbind
>>  >
>>  >or unbind the glue driver:
>>  >
>>  >root@...35x-evm:/sys/bus/platform/drivers/musb-dsps# echo
>>  >47401400.usb > unbind
>>  >
>>  >musb_gadget_pullup() is called in both cases.
>>  >
>>  >[ 3880.597014] [<bf444ab0>] (musb_gadget_pullup [musb_hdrc]) from
>>  >[<bf402cbc>] (usb_gadget_disconnect+0x3c/0xf4 [udc_core])
>>  >[ 3880.607959] [<bf402cbc>] (usb_gadget_disconnect [udc_core])
>>  >from [<bf403b28>] (usb_gadget_remove_driver+0x4c/0x90 [udc_core])
>>  >[ 3880.619338] [<bf403b28>] (usb_gadget_remove_driver [udc_core])
>>  >from [<bf403d20>] (usb_del_gadget_udc+0x5c/0xc0 [udc_core])
>> 
>>  In my case this stops here, usb_del_gadget_udc() does not call
>>  usb_gadget_remove_driver(), that's why the pullup is never disabled.
>> 
>>  I guess that's because udc->driver is NULL; I'm testing with
> 
> then the pullup should be disable by now.
> 
>>  CONFIG_USB_CONFIGFS,
>>  and I don't configure anything in sysfs before unbinding the driver.
> 
> I didn't check on this, but I could imagine that
> - when a configfs gadget is bound to the udc, .pullup() is called;
> - when the configfs gadget is unbound from the udc, .pullup should be
>   called again to disable the pullup.

An important thing that I did not mention, is that the SoC boots from 
USB,
so the pullup is active before the musb driver loads. Since in my case a
configfs gadget is never bound, then .pullup() is never called, and when
I unbind the driver the pullup is still enabled.

-Paul