Re: [PATCH] Add Apple Carplay driver

From: Chunfeng Yun <chunfeng.yun@mediatek.com>
To: Matthew Dharm <mdharm-usb@one-eyed-alien.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Serge Semin <fancer.lancer@gmail.com>,
	Guenter Roeck <linux@roeck-us.net>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Alan Stern" <stern@rowland.harvard.edu>,
	<linux-kernel@vger.kernel.org>, <linux-usb@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH] Add Apple Carplay driver
Date: Wed, 14 Mar 2018 16:18:55 +0800	[thread overview]
Message-ID: <1521015535.3717.26.camel@mhfsdcap03> (raw)
In-Reply-To: <CAA6KcBAnLYZ2UyUB6Ecv96D0zWhmce2BMmA_iWx04njeNYsd9w@mail.gmail.com>

On Tue, 2018-03-13 at 23:53 -0700, Matthew Dharm wrote:
> Why is this a kernel-level driver, rather than a userspace application
> that uses libusb to send the single vendor-specific command required?
> Since this command would be applicable to many CarPlay devices, with
> many different VID/PIDs, it would seem to make more sense as a
> userspace app that took a reference to a USB device or VID/PID.
Sorry, I'm not familiar with libusb.
But after I roughly read a simple example using libusb, it indeed can be
realized by a userspace driver.

Thanks for your useful comments

> 
> Matt
> 
> On Tue, Mar 13, 2018 at 11:02 PM, Chunfeng Yun
> <chunfeng.yun@mediatek.com> wrote:
> > From bf48dcd9cb254576cfea373c9a5d2ab996408895 Mon Sep 17 00:00:00 2001
> > From: Chunfeng Yun <chunfeng.yun@mediatek.com>
> > Date: Tue, 13 Mar 2018 11:47:38 +0800
> > Subject: [PATCH] Add Apple Carplay driver
> >
> > Some Apple devices which support Carplay can enter USB Host Mode from USB
> > Device Mode after receiving a specific USB Vendor Request. There is a
> > requirement apply to accesssories that support the USB dual role switch
> > feature, and must have a USB-A receptacle that is capable of functioning
> > in both USB Host and USB Device roles.
> > It means that the driver should supports manual Dual-Role switch, due to
> > no IDDIG pin is avaliable.
> >
> > There is no suitable place to add this spicific USB Vendor Request, so
> > here I extract a single driver which allow user force to send it by a debug
> > interface when need it, and keep it independent on USB Dual-Role Controller
> > Drivers.
> > But to implement carplay feature, there are some requirments for USB Dual-Role
> > Driver:
> > 1. supports manual dual-role switch, such as, by a debug interface;
> > 2. keep vbus alive even when switch host into device mode;
> >
> > More information please refer to "Chapter 46. USB Role Switch" in
> > MFI Accessroy Interface Specification.pdf
> >
> > Chunfeng Yun (1):
> >   usb: misc: supports Apple Carplay driver
> >
> >  drivers/usb/misc/Kconfig   |    9 +++
> >  drivers/usb/misc/Makefile  |    1 +
> >  drivers/usb/misc/carplay.c |  193 ++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 203 insertions(+)
> >  create mode 100644 drivers/usb/misc/carplay.c
> >
> > --
> > 1.7.9.5
> >
> >
> > --
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> 
> 
>