linux-kernel - Re: [PATCH 1/2] extcon: extcon-dra7xx: Add extcon driver for USB ID detection

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Date:	Tue, 20 Aug 2013 10:53:35 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	George Cherian <george.cherian@...com>
CC:	balbi@...com, myungjoo.ham@...sung.com, cw00.choi@...sung.com,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, grant.likely@...aro.org,
	rob@...dley.net, ian.campbell@...rix.com, mark.rutland@....com,
	pawel.moll@....com, rob.herring@...xeda.com,
	linux-omap@...r.kernel.org, linux-usb@...r.kernel.org,
	bcousson@...libre.com
Subject: Re: [PATCH 1/2] extcon: extcon-dra7xx: Add extcon driver for USB
 ID detection

On 08/20/2013 12:55 AM, George Cherian wrote:
> Hi Stephen,
> 
> Thanks for your review.
> 
> On 8/20/2013 1:01 AM, Stephen Warren wrote:
> 
>> On 08/16/2013 04:13 AM, George Cherian wrote:
>>> Adding extcon driver for USB ID detection to dynamically
>>> configure USB Host/Peripheral mode.
>>> diff --git
>>> a/Documentation/devicetree/bindings/extcon/extcon-dra7xx.txt
>>> b/Documentation/devicetree/bindings/extcon/extcon-dra7xx.txt
>>> +EXTCON FOR DRA7xx
>>> +
>>> +Required Properties:
>> Please at lest explain what a DRA7xxx is, and the purpose of the HW
>> module this binding describes.
> 
> DRA7xx is the SoC name and the USB VID  detection is implemented via gpio's
> Basically it does only ID detection via GPIO and there is no VBUS
> detection in h/w.

If there's no SoC-specific HW, then the binding has nothing to do with
the SoC; it's entirely generic.

I think instead, you need to define a generic "gpio-usb-vid" binding
instead.

Otherwise, ever SoC that doesn't have explicit USB VID detection HW is
going to re-invent the exact same binding, with pointless differences,
rather than using a single generic binding.

>>> + - compatible : Should be "ti,dra7xx-usb"
>>
>> If this is a USB VID detector rather than a full USB host controller,
>> then "usb" in the binding is a bit over-reaching. Perhaps "-usb-vid" or
>> "-usb-vid-detector" would be more accurate.
> 
> This will be renamed to dra7xx-extcon.

So no, that rename doesn't sound correct.

>>> + - gpios : phandle to ID pin and interrupt gpio.
>>
>> Why does the interrupt line need to be included in a list of GPIOs?
> 
> ID pins are connected to pcf8575, and the pcf8575's interrupt line is
> inturn connected to
> gpio bank6 pin 11, we use this gpio interrupt to detect the ID pin change.

In that case, the PCF8575 node needs to be a GPIO controller and an IRQ
controller, as does the driver for the PCF8575. This binding should have
a single entry in the gpios property, and the driver can call
gpio_to_irq() on that so it knows which IRQ to request.
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