linux-kernel - Re: [External] Re: [PATCH v5 0/8] Add MA USB Host driver

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Message-ID: <20200529124843.GA1339@bug>
Date:   Fri, 29 May 2020 14:48:43 +0200
From:   Pavel Machek <pavel@....cz>
To:     Vladimir Stankovic <vladimir.stankovic@...playlink.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, mausb-host-devel@...playlink.com
Subject: Re: [External] Re: [PATCH v5 0/8] Add MA USB Host driver

Hi!

> >>>> MA USB protocol used by MA USB Host driver has been implemented in
> >>>> accordance with MA USB Specification Release 1.0b.
> >>>
> >>> Is that a USB-released spec?
> >> Correct, document is being maintained by USB IF and is publicly available.
> >> However, I just noticed a typo, correct version is 1.0a. Will correct.
> >>
> >> In short, MA USB Specification defines an MA USB protocol that performs USB
> >> communication via any communication medium. As such, it defines how to pack
> >> USB data within MA USB payload, and how to communicate with remote MA USB device.

Ok

> >> Userspace code is not publicly available. However, in short, it's purpose is
> >> twofold, to provide interface to application layer, and to prepare MA USB packets
> >> that will be used by remote device.
> > 
> > So you want us to take a one-off char-driver kernel code for a closed
> > source userspace application for a public spec?  That feels really
> > really odd, if not actually against a few licenses.  I hate to ask it,
> > but are your lawyers ok with this?

More importantly... does that work?

Userland is okay for communication setup, but if userspace is involved with every packet
being sent... It will deadlock.

One example: attach mass storage device over MUSB, put swap there; what happens if your
userland helper is now swapped out?

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html