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Date:   Fri, 19 May 2023 10:49:49 -0400
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Badhri Jagan Sridharan <badhri@google.com>
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>
Subject: Re: [PATCH v2] usb: gadget: udc: core: Offload usb_udc_vbus_handler
 processing
Message-ID: <c181c8ef-f342-4a31-9b8c-e1fa14ad214e@rowland.harvard.edu>
References: <20230519043041.1593578-1-badhri@google.com>
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On Fri, May 19, 2023 at 04:30:41AM +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.

Look, this is way overkill.

usb_udc_vbus_handler() has only two jobs to do: set udc->vbus and call 
usb_udc_connect_control().  Furthermore, it gets called from only two 
drivers: chipidea and max3420.

Why not have the callers set udc->vbus themselves and then call 
usb_gadget_{dis}connect() directly?  Then we could eliminate 
usb_udc_vbus_handler() entirely.  And the unnecessary calls -- the ones 
causing deadlocks -- from within udc_start() and udc_stop() handlers can 
be removed with no further consequence.

This approach simplifies and removes code.  Whereas your approach 
complicates and adds code for no good reason.

Alan Stern