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From:   Badhri Jagan Sridharan <badhri@google.com>
Date:   Wed, 17 May 2023 10:19:25 -0700
Message-ID: <CAPTae5JB2LLEF7ZNaJxMnF==8WCWoEYvmF_FK3F=BDq0Hko0xQ@mail.gmail.com>
Subject: Re: [PATCH v1] usb: gadget: udc: core: Offload usb_udc_vbus_handler processing
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     gregkh@linuxfoundation.org, colin.i.king@gmail.com,
        xuetao09@huawei.com, quic_eserrao@quicinc.com,
        water.zhangjiantao@huawei.com, peter.chen@freescale.com,
        balbi@ti.com, francesco@dolcini.it, alistair@alistair23.me,
        stephan@gerhold.net, bagasdotme@gmail.com, luca@z3ntu.xyz,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org,
        Francesco Dolcini <francesco.dolcini@toradex.com>
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On Wed, May 17, 2023 at 7:44=E2=80=AFAM Alan Stern <stern@rowland.harvard.e=
du> wrote:
>
> On Wed, May 17, 2023 at 11:59:55AM +0000, Badhri Jagan Sridharan wrote:
> > chipidea udc calls usb_udc_vbus_handler from udc_start gadget
> > ops causing a deadlock. Avoid this by offloading usb_udc_vbus_handler
> > processing.
>
> Surely that is the wrong approach.
>
> The real problem here is that usb_udc_vbus_handler() gets called from
> within a udc_start routine.  But this is totally unnecessary, because
> the UDC core will call usb_udc_connect_control_locked() itself, later on
> during gadget_bind_driver().

Hi Alan,

usb_udc_vbus_handler sets the udc->vbus flag as well apart from
calling usb_udc_connect_control_locked().  So, removing usb_udc_vbus_handle=
r
from chip specific start callback might prevent the controller from
starting.

void usb_udc_vbus_handler(struct usb_gadget *gadget, bool status)
{
struct usb_udc *udc =3D gadget->udc;

mutex_lock(&udc->connect_lock);
if (udc) {
udc->vbus =3D status;
usb_udc_connect_control_locked(udc);

Thanks,
Badhri


>
> So a proper solution would be simply to remove the unnecessary
> usb_udc_vbus_handler() call from the chipidea driver (and similarly for
> the max3420_udc driver).
>
> Similar changes may be needed in these drivers' udc_stop routines.
>
> Alan Stern