linux-kernel - Re: [PATCH] Add Apple Carplay driver

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Message-ID: <CAA6KcBAnLYZ2UyUB6Ecv96D0zWhmce2BMmA_iWx04njeNYsd9w@mail.gmail.com>
Date:   Tue, 13 Mar 2018 23:53:15 -0700
From:   Matthew Dharm <mdharm-usb@...-eyed-alien.net>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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] Add Apple Carplay driver

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.

Matt

On Tue, Mar 13, 2018 at 11:02 PM, Chunfeng Yun
<chunfeng.yun@...iatek.com> wrote:
> From bf48dcd9cb254576cfea373c9a5d2ab996408895 Mon Sep 17 00:00:00 2001
> From: Chunfeng Yun <chunfeng.yun@...iatek.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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-- 
Matthew Dharm
Former Maintainer, USB Mass Storage driver for Linux