Subject: Re: [PATCH/RFT 07/12] USB: ohci-da8xx: Request gpios and handle
 interrupt in the driver
To: ahaslam@baylibre.com, gregkh@linuxfoundation.org, robh+dt@kernel.org,
        nsekhar@ti.com, stern@rowland.harvard.edu, khilman@baylibre.com,
        sshtylyov@ru.mvista.com
References: <1475858577-10366-1-git-send-email-ahaslam@baylibre.com>
 <1475858577-10366-8-git-send-email-ahaslam@baylibre.com>
Cc: linux-usb@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
From: David Lechner <david@lechnology.com>
Message-ID: <22f1532a-b651-3330-b2ce-9a64a35c85af@lechnology.com>
Date: Mon, 10 Oct 2016 18:18:46 -0500
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On 10/07/2016 11:42 AM, ahaslam@baylibre.com wrote:
> From: Axel Haslam <ahaslam@baylibre.com>
>
> Currently requesting the vbus and overcurrent gpio is handled on
> the board specific file. But this does not play well moving to
> device tree.
>
> In preparation to migrate to a device tree boot, handle requesting
> gpios and overcurrent interrupt on the usb driver itself, thus avoiding
> callbacks to arch/mach*
>

Instead of using gpios, it seems like it would be better to use a 
regulator here. I don't know of any real-life cases, but who is to say 
someone will not design a board that uses a regulator controlled by I2C 
instead of gpios or something like that.

Then, boards that don't have gpios can just use a fixed regulator (or 
you can make the regulator optional). Using a regulator would also allow 
users to decide how to respond to overcurrent events (by supplying their 
own regulator driver) instead of the behavior being dictated by the ohci 
driver.

In my particular area of interest (LEGO MINDSTORMS EV3), the 5V 
(hardware) regulator for VBUS does use gpios, but the 5V is also shared 
with the LEGO input and output ports. So what I would ultimately like to 
be able to do is have userspace notified of an overcurrent event and let 
userspace decided when to turn the vbus back on. For example, someone 
might plug something into one of the LEGO input or output ports that 
causes a short circuit. I would like to display a notification to the 
user and wait for them to correct the problem and then press a button to 
turn the power back on.

This will require some modifications to the regulator subsystem though. 
I actually started work on this a while back, but haven't had the time 
to pursue it any farther.

Here are my WIP patches in case there is any interest:
* 
https://github.com/dlech/ev3dev-kernel/commit/541a42b3b8ed639e95bbc835df3292f80190c789
* 
https://github.com/dlech/ev3dev-kernel/commit/2ba99b1ad6a06c944dd33a073f54044e71b75ae6
* 
https://github.com/dlech/ev3dev-kernel/commit/cdb03caa50e64931d4f2836c648739aa4385ed3b
* 
https://github.com/dlech/ev3dev-kernel/commit/9d6b50cde34b51309c74d97c26b1430c7ff6aa0f