linux-kernel - Re: [PATCH 1/3] HID: add driver for Valve Steam Controller

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Date:   Thu, 15 Feb 2018 00:29:57 +0100
From:   Rodrigo Rivas Costa <rodrigorivascosta@...il.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>, linux-input@...r.kernel.org
Subject: Re: [PATCH 1/3] HID: add driver for Valve Steam Controller

On Wed, Feb 14, 2018 at 03:45:14PM +0100, Benjamin Tissoires wrote:
> I think I had a look at this a while ago, and didn't want to interfere
> with SteamOS regarding this. I think your patch should be fine in that
> regard, but have you tried SteamOS on a kernel patched with your
> series? Does it behave properly or will it break?

Well, SteamOS is just a modified Debian with the Steam Client running in
Big Picture mode (fullscreen). I tried the Steam Client with this driver
and it works just fine: 
- The first thing the Steam Client (SC) does is to disable the virtual
  keyboard and mouse, so not creating those input devices make no
  difference.
- Input events are sent both to the libusb (or whatever SC uses) and
  this driver.
- The only source of conflict would be in sending commands to the
  controller. But currently the only command sent is the get_serial, and
  that seems to do no harm.

> > +
> > +       hid_info(hdev, "Steam Controller connected");
> > +
> > +       input = input_allocate_device();
> 
> Don't you need one input node per wireless gamepad too?
> 
No, the wired and wireless methods are two different USB devices.
The wireless adaptor is a small usb device that creates 4 HID interfaces
for the 4 to-be-connected controllers. When the 'connected' event
arrives on one of those interfaces we will create one input device.
Another controller connected will use a different interface so another
unrelated input device will be created.

The wired adaptor is the controller connected directly to USB: it
creates one HID inteface and one input device directly.

Anyway, one steam_device will contain 0 or 1 input_device.

> > +       input->name = "Steam Controller";
> 
> In case of the wireless controllers, you might want to personalize this a bit.

Do you mean e.g. "Wireless Steam Controller"? Would be wise to add the serial
number here (from PATCH 2/3?)? Or is the 'uniq' enough for that?

> > +       input_set_abs_params(input, ABS_Z, 0, 255, 0, 0);
> > +       input_set_abs_params(input, ABS_RZ, 0, 255, 0, 0);
> > +       input_set_abs_params(input, ABS_X, -32767, 32767, 0, 0);
> > +       input_set_abs_params(input, ABS_Y, -32767, 32767, 0, 0);
> 
> You are also probably missing the resolution bits. We need to
> accurately report the physical dimensions to the user space (thanks to
> the resolution)
> 
> > +       input_set_abs_params(input, ABS_RX, -32767, 32767, 0, 0);
> > +       input_set_abs_params(input, ABS_RY, -32767, 32767, 0, 0);
> 
> What do RX/RY correspond to?

This gamepad has 1 joystick and 2 touchpads (lpad and rpad).
I'm mapping the joystick/lpad to ABS_X/ABS_Y and the rpad to
ABS_RX/ABS_RY.

About the resolution, I looked around other drivers and many have 0 as
resolution... is it necessary only in the pads or the joystick too?
And what are the units of that value?
For reference, the pads are round and exactly 40 mm in diameter.

Why the lpad and the joystick are mapped to the same axes? Well, because
the device returns them at the same offset. We could make them
apart by using bits 10.3 (lpad_touch) and 10.7 (lpad_and_joy) but I
don't think it is worth it... you use the joystick and the lpad with the
same thumb!

> Anyway. Thanks for the driver, there are a few bits to fix, nothing
> scary though.

Great, I'll correct all those issues and resubmit the patches in a few
days. It is my very first driver and I'm still a bit slow...

Thank you for your attention!
Rodrigo.