linux-kernel - Re: [PATCH] usb-musb: keep VBUS on when device is disconnected

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Message-Id: <63FD9E13-2B70-485C-80A7-206BEC16905A@tecnorama.it>
Date:   Mon, 27 Mar 2017 18:20:29 +0200
From:   Moreno Bartalucci <moreno.bartalucci@...norama.it>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Bin Liu <b-liu@...com>, Lars Melin <larsm17@...il.com>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alessio Igor Bogani <abogani@...nel.org>
Subject: Re: [PATCH] usb-musb: keep VBUS on when device is disconnected

> Il giorno 27 mar 2017, alle ore 16:30, Tony Lindgren <tony@...mide.com> ha scritto:
> 
> […]
> I wonder if the following test patch allows the mode changing
> devices to been properly found? Of course it's just for testing,
> and scanning for devices takes now 5 seconds.. But it might
> provide clues why musb thinks no devices are connected and we
> cut VBUS.
> 
> […]

Hi Tony,

thanks for your patch.

I tested it with both current mainline kernel and my “production” kernel (4.9.13): they have the same behaviour.

During boot, vbus is first asserted, then removed for a slightly longer time than before (most likely 5 seconds now), then reasserted.

When my device is mode-switched, it is working properly with your patch.

If I understood your patch, however, if the device (anyone, not just my one) takes longer to switch, VBUS is deasserted anyway.

Although this patch is working for me, personally I would prefer a solution which would not deassert VBUS. At least on a host only port. Honestly I don’t know how a dual role port should work.

Regards,

Moreno