Re: [PATCH/RFT 07/12] USB: ohci-da8xx: Request gpios and handle interrupt in the driver

From: David Lechner
Date: Mon Oct 10 2016 - 19:18:34 EST

On 10/07/2016 11:42 AM, ahaslam@xxxxxxxxxxxx wrote:
From: Axel Haslam <ahaslam@xxxxxxxxxxxx>

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: