MIME-version: 1.0
Content-type: text/plain; charset=windows-1252; format=flowed
Content-transfer-encoding: 8BIT
Message-id: <55CCFCA6.9070907@samsung.com>
Date: Thu, 13 Aug 2015 22:23:02 +0200
From: Krzysztof Opasiak <k.opasiak@samsung.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101
 Thunderbird/31.4.0
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Amit Pundir <amit.pundir@linaro.org>, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-api@vger.kernel.org, Mike Lockwood <lockwood@android.com>,
        Benoit Goby <benoit@android.com>, Colin Cross <ccross@android.com>,
        =?windows-1252?Q?Arve_Hj=F8nnev=E5g?= <arve@android.com>,
        Peter Oh <poh@broadcom.com>, Greg Hackmann <ghackmann@google.com>,
        Badhri Jagan Sridharan <Badhri@google.com>,
        Android Kernel Team <kernel-team@android.com>,
        Jonathan Corbet <corbet@lwn.net>, Felipe Balbi <balbi@ti.com>,
        Andrzej Pietrasiewicz <andrzej.p@samsung.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Yegor Yefremov <yegorslists@googlemail.com>,
        Philippe Reynes <tremyfr@gmail.com>,
        John Stultz <john.stultz@linaro.org>,
        Sumit Semwal <sumit.semwal@linaro.org>
Subject: Re: [RFC][PATCH 1/2] usb: gadget: configfs: add MTP function
References: <1439493140-22207-1-git-send-email-amit.pundir@linaro.org>
 <1439493140-22207-2-git-send-email-amit.pundir@linaro.org>
 <55CCF156.8010302@samsung.com> <20150813195748.GB30092@kroah.com>
In-reply-to: <20150813195748.GB30092@kroah.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 4278
Lines: 93


On 08/13/2015 09:57 PM, Greg Kroah-Hartman wrote:
> On Thu, Aug 13, 2015 at 09:34:46PM +0200, Krzysztof Opasiak wrote:
>> Hello,
>>
>> On 08/13/2015 09:12 PM, Amit Pundir wrote:
>>> his MTP function is based on years of work originally done in the
>>> Android kernel tree by:
>>>      Mike Lockwood<lockwood@android.com>
>>>      Benoit Goby<benoit@android.com>
>>>      Colin Cross<ccross@android.com>
>>>      Arve Hj?nnev?g<arve@android.com>
>>>      Peter Oh<poh@broadcom.com>
>>>      Greg Hackmann<ghackmann@google.com>
>>>      Badhri Jagan Sridharan<Badhri@google.com>
>>> I've folded the series up to make it easier to review, and to provide
>>> a coherent patch description.
>>>
>>> Post Gingerbread (Android v2.3), Android dropped USB Mass Storage
>>> in favor of Media Transfer Protocal (MTP), which is widely used for
>>> transferring media files to digital music players and similar
>>> applications. This USB gadget function implements MTP functionalty.
>>>
>>> Historically this function has been a part of Android composite
>>> gadget driver. Android composite driver was Android's solution
>>> for dynamic gadget function switching prior to the ConfigFS gadget
>>> being merged. There were failed few attempts in past
>>> http://marc.info/?l=linux-usb&m=132451695808552  to upstream Android
>>> composite driver as well. Now this Android MTP gadget function has been
>>> re-implemented so as to be used as a generic ConfigFS function instead.
>>>
>>> Again, many thanks to Mike, Benoit, Colin, Arve, Peter, Greg and Badhri,
>>> as they are the real authors of this work. However, I've folded their
>>> patches together and modified it enough that I don't want them to be
>>> blamed for any mistakes I've made condensing their patches down.
>>>
>>> Cc: Mike Lockwood<lockwood@android.com>
>>> Cc: Benoit Goby<benoit@android.com>
>>> Cc: Colin Cross<ccross@android.com>
>>> Cc: Arve Hj?nnev?g<arve@android.com>
>>> Cc: Peter Oh<poh@broadcom.com>
>>> Cc: Greg Hackmann<ghackmann@google.com>
>>> Cc: Badhri Jagan Sridharan<Badhri@google.com>
>>> Cc: Android Kernel Team<kernel-team@android.com>
>>> Cc: Greg Kroah-Hartman<gregkh@linuxfoundation.org>
>>> Cc: Jonathan Corbet<corbet@lwn.net>
>>> Cc: Felipe Balbi<balbi@ti.com>
>>> Cc: Andrzej Pietrasiewicz<andrzej.p@samsung.com>
>>> Cc: Laurent Pinchart<laurent.pinchart@ideasonboard.com>
>>> Cc: Yegor Yefremov<yegorslists@googlemail.com>
>>> Cc: Philippe Reynes<tremyfr@gmail.com>
>>> Cc: John Stultz<john.stultz@linaro.org>
>>> Cc: Sumit Semwal<sumit.semwal@linaro.org>
>>> Signed-off-by: Amit Pundir<amit.pundir@linaro.org>
>>
>> In my humble opinion adding such function to Linux kernel doesn't make any
>> sense. By design, MTP is a protocol which requires access to userspace
>> features esp. file system. It is very important to run MTP daemon with
>> suitable user and LSM label and many many other issues which should be
>> handled by userspace access policy.
>>
>> Moreover this is not a fully functional USB function but only some interface
>> which can be used by mtp-responder (mtp-daemon - call it as you like) to
>> communicate with host. As we have FunctionFS which allows to implement any
>> USB function in as a userspace service. As MTP nature is more related to
>> userspace I think that porting MTP daemon to use this is a right way to go.
>> This should be much more reasonable than adding new function which also
>> requires daemon for proper working. So why add another interface while we
>> can use a generic one?
>
> Isn't there already a userspace MTP daemon that uses the existing
> functionfs for usb gadgets?  I thought I remember seeing that
> somewhere...
>

I know for sure that ADB and SDB has been ported to use functionfs. I 
can even see ADB with ffs backend working on my nexus 9 with 3.10 kernel.

I've seen such mtp-responder implementation but that time it has not 
been published to open source. I don't know what is the current state...

Best regards,

-- 
Krzysztof Opasiak
Samsung R&D Institute Poland
Samsung Electronics
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/