linux-kernel - Re: [PATCH 0/5] extcon: usb: Introduce USB GPIO extcon driver. Fix DRA7 USB.

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Message-ID: <20150122202907.GC22288@saruman.tx.rr.com>
Date:	Thu, 22 Jan 2015 14:29:07 -0600
From:	Felipe Balbi <balbi@...com>
To:	Roger Quadros <rogerq@...com>
CC:	<balbi@...com>, <tony@...mide.com>, <myungjoo.ham@...sung.com>,
	<cw00.choi@...sung.com>, <george.cherian@...com>, <nsekhar@...com>,
	<devicetree@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/5] extcon: usb: Introduce USB GPIO extcon driver. Fix
 DRA7 USB.

On Thu, Jan 22, 2015 at 04:57:56PM +0200, Roger Quadros wrote:
> 
> On 22/01/15 15:32, Roger Quadros wrote:
> > Felipe,
> > 
> > On 20/01/15 21:02, Felipe Balbi wrote:
> >> On Mon, Jan 19, 2015 at 07:52:17PM +0200, Roger Quadros wrote:
> >>> Hi,
> >>>
> >>> On DRA7 EVMs the USB ID pin is connected to a GPIO line. The USB drivers
> >>> (dwc3 + dwc3-omap) depend on extcon framework to get the USB cable state
> >>> (USB or USB-Host) to put the controller in the right mode.
> >>>
> >>> There were earlier attempts [1] to get this working by trying to patch up
> >>> the existing GPIO extcon driver.
> >>>
> >>> This series attemts to take a different approach by introducing a new
> >>> USB specific extcon driver to handle the USB ID GPIO pin and
> >>> interpret a right USB cable state.
> >>>
> >>> The reasoning to introduce this new driver is:
> >>> 1) The existing GPIO extcon driver doesn't understand USB cable states
> >>> and it can't handle more than one cable per instance.
> >>>    
> >>> For the USB case we need to handle at least 2 cable states.
> >>>     a) USB (attach/detach)
> >>>     b) USB-Host (attach/detach)
> >>> and could possible include more states like
> >>>     c) Fast-charger (attach/detach)
> >>>     d) Slow-charger (attach/detach)
> >>>     
> >>> 2) This USB specific driver can be easily updated in the future to
> >>> handle VBUS events, or charger detect events, in case it happens
> >>> to be available on GPIO for any platform.
> >>>
> >>> 3) The DT implementation is very easy. You just need one extcon node per USB
> >>> instead of one extcon node per cable state as in case of [1].
> >>>
> >>> 4) The cable state string doesn't need to be encoded in the device tree
> >>> as in case of [1].
> >>>
> >>> 5) With only ID event available, you can simulate a USB-peripheral attach
> >>> when USB-Host is detacted instead of hacking the USB driver to do the same.
> >>>
> >>> Tested on DRA7-evm and DRA72-evm.
> >>
> >> while at that, you might want to patch X15 too.
> >>
> > USB2 port is meant for peripheral use only. ID pin from USB port is not connected to GPIO.
> > 
> 
> OK answering myself here :).
> Peripheral mode doesn't work on x15-bb as the USB driver (dwc3-omap)
> doesn't set the mailbox correctly even when dwc3 node is set as otg = "peripheral".
> 
> Looks like we need to implement usb-gpio-extcon for x15 even though ID is hard coded.

right, another option is to have dwc3-omap read the child's DTS to check
dr_mode and hardcode things based on that.

-- 
balbi

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