linux-kernel - Re: [PATCH v3] USB: hub.c: decrease the number of attempts of enumeration scheme

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Message-ID: <20200915144843.GB1002979@rowland.harvard.edu>
Date:   Tue, 15 Sep 2020 10:48:43 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Eugeniu Rosca <erosca@...adit-jv.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, andrew_gabbasov@...tor.com,
        Baxter Jim <jim_baxter@...tor.com>,
        "Natsume, Wataru \(ADITJ/SWG\)" <wnatsume@...adit-jv.com>,
        "Nishiguchi, Naohiro \(ADITJ/SWG\)" <nnishiguchi@...adit-jv.com>,
        浅野恭史 <yasano@...adit-jv.com>,
        kernel test robot <rong.a.chen@...el.com>,
        yasushi asano <yazzep@...il.com>,
        Martin Mueller <Martin.Mueller5@...bosch.com>,
        Eugeniu Rosca <roscaeugeniu@...il.com>
Subject: Re: [PATCH v3] USB: hub.c: decrease the number of attempts of
 enumeration scheme

On Tue, Sep 15, 2020 at 11:45:31AM +0200, Eugeniu Rosca wrote:
> Dear Alan,
> Dear Greg,
> 
> On Fri, Sep 11, 2020 at 11:12:28AM -0400, Alan Stern wrote:
> 
> > The thing is, I'm afraid that without these retry loops, some devices
> > will stop working.  If that happens, we will not be able to keep this
> > patch in place; we will just have to accept that we fail the PET test.
> > 
> > Alan Stern
> 
> Does this mean that Linux community leaves no choice but to ship a
> forked kernel (with no chance of alignment to upstream) for
> organizations which design embedded devices where USB plays a key
> role, hence requires passing the USB-IF Compliance Program [*]?
> 
> Is there hope to give users a knob (build-time or run-time) which would
> enable the behavior expected and thoroughly described in compliance
> docs, particularly chapter "6.7.22 A-UUT Device No Response for
> connection timeout" of "USB On-The-Go and Embedded Host Automated
> Compliance Plan" [**]?

It is possible to add a build-time Kconfig option that would control the 
maximum number of port initialization attempts.  But let's start with 
testing the patch I sent you.  After all, the first step is to get 
something that does what you want correctly.

Alan Stern