linux-kernel - Re: [PATCH] usb: misc: supports Apple Carplay driver

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Message-ID: <1521015652.3717.28.camel@mhfsdcap03>
Date:   Wed, 14 Mar 2018 16:20:52 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Matthias Brugger <matthias.bgg@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Alan Stern" <stern@...land.harvard.edu>,
        <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH] usb: misc: supports Apple Carplay driver

On Wed, 2018-03-14 at 07:16 +0100, Greg Kroah-Hartman wrote:
> On Wed, Mar 14, 2018 at 02:02:36PM +0800, Chunfeng Yun wrote:
> > The driver is used to support Apple carplay feature by a debugfs
> > interface which can force the driver to send a USB Vendor Request
> > of "Apple Device to Host Mode Switch" to switch Apple Device
> > into host mode.
> 
> While I am all for crazy debugfs interfaces, I would _strongly_ suggest
> not doing that here for the main API to the device.  I know Android is
> trying to prevent any new devices from even enabling debugfs, and as the
> file system requires root permissions by default, you are forcing any
> user of your new api to run as root, which is not a good idea either.
> 
> Given that all you are doing here is a single usb control message, why
> does this even need to be a kernel driver at all?  Can't you do the same
> thing from userspace with a simple libusb/usbfs program?  Or even a
> simple script?
Ok, I'll abandon this patch, and do it by libusb

Thanks a lot

> 
> thanks,
> 
> greg k-h