linux-kernel - Re: [PATCH v10 0/6] Introduced new Cadence USBSS DRD Driver.

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Date:   Mon, 19 Aug 2019 10:19:44 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Roger Quadros <rogerq@...com>
cc:     Pawel Laszczak <pawell@...ence.com>,
        <felipe.balbi@...ux.intel.com>, <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <jbergsagel@...com>, <nsekhar@...com>, <nm@...com>,
        <sureshp@...ence.com>, <jpawar@...ence.com>, <kurahul@...ence.com>,
        <aniljoy@...ence.com>
Subject: Re: [PATCH v10 0/6] Introduced new Cadence USBSS DRD Driver.

On Mon, 19 Aug 2019, Roger Quadros wrote:

> On 15/08/2019 17:39, Alan Stern wrote:
> > On Thu, 15 Aug 2019, Roger Quadros wrote:
> > 
> >> Felipe & Alan,
> >>
> >> On 21/07/2019 21:32, Pawel Laszczak wrote:
> >>> This patch introduce new Cadence USBSS DRD driver to linux kernel.
> >>>
> >>> The Cadence USBSS DRD Controller is a highly configurable IP Core which
> >>> can be instantiated as Dual-Role Device (DRD), Peripheral Only and
> >>> Host Only (XHCI)configurations.
> >>>
> >>> The current driver has been validated with FPGA burned. We have support
> >>> for PCIe bus, which is used on FPGA prototyping.
> >>>
> >>> The host side of USBSS-DRD controller is compliance with XHCI
> >>> specification, so it works with standard XHCI Linux driver.
> >>
> >> While testing this driver I encountered the following issue if I do the following.
> >>
> >> 1) USB port is "otg" and nothing connected so it is in IDLE mode to begin with.
> >>    i.e. HCD & UDC not registered.
> >>
> >> 2) Load mass storage gadget with backing medium.
> >>    > modprobe g_mass_storage file=lun stall=0
> >>
> >> [   28.172142] udc-core: couldn't find an available UDC - added [g_mass_storage] to list of pending drivers
> >>
> >> 3) Connect port to PC host

...

> >> [   30.786313] Mass Storage Function, version: 2009/09/11
> >> [   30.791455] LUN: removable file: (no medium)
> >> [   31.039497] lun0: unable to open backing file: 500M.bin

> >> Is opening the backing file from irq_thread_fn the issue here?
> >> If yes, how to resolve this?
> > 
> > I would guess that it probably is related to that.
> > 
> > In any case, the backing filename should be an explicit complete path.  
> > Who knows what the current directory will be when the actual open call
> > takes place?
> 
> This seems to be the case. It works fine with complete path.
> 
> Do we need to care about this in the mass storage gadget or just
> rely on the user to provide the full path?

I think it's okay to rely on the user to provide the full path.

Alan Stern