linux-kernel - Re: [PATCH v1] usb: gadget: udc: core: Offload usb_udc_vbus

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Date:   Wed, 17 May 2023 10:19:25 -0700
From:   Badhri Jagan Sridharan <badhri@...gle.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     gregkh@...uxfoundation.org, colin.i.king@...il.com,
        xuetao09@...wei.com, quic_eserrao@...cinc.com,
        water.zhangjiantao@...wei.com, peter.chen@...escale.com,
        balbi@...com, francesco@...cini.it, alistair@...stair23.me,
        stephan@...hold.net, bagasdotme@...il.com, luca@...tu.xyz,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org,
        Francesco Dolcini <francesco.dolcini@...adex.com>
Subject: Re: [PATCH v1] usb: gadget: udc: core: Offload usb_udc_vbus_handler processing

On Wed, May 17, 2023 at 7:44 AM Alan Stern <stern@...land.harvard.edu> 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_handler
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 = gadget->udc;

mutex_lock(&udc->connect_lock);
if (udc) {
udc->vbus = 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