linux-kernel - Re: [RFC PATCH] input: Add wiichuck driver

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Message-ID: <20110516183124.GA4875@ponder.secretlab.ca>
Date:	Mon, 16 May 2011 12:31:24 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [RFC PATCH] input: Add wiichuck driver

On Mon, May 16, 2011 at 09:44:27AM -0700, Dmitry Torokhov wrote:
> Hi Grant,
> 
> On Thu, May 12, 2011 at 06:29:44AM +0200, Grant Likely wrote:
> > This patch adds a driver for the Nintendo Nunchuck (wiimote accessory)
> > attached to an i2c bus via something like a wiichuck adapter board
> > from Sparkfun.
> > 
> > Signed-off-by: Grant Likely <grant.likely@...retlab.ca>
> > ---
> > 
> > This is RFC because the driver doesn't completely work yet.  The
> > joystick and buttons work fine.  There is a bug with the accelerometer
> > reporting though (nothing gets reported), and I'm not even sure I'm
> > using the right input type for reporting accelerometer values.
> 
> Looks quite reasonable and I think that ABS_Rx is reasonable events for
> accelerometer in this particular case.
> 
> A few more comments below.

Hi Dmitry, thanks for the review.  Replies below.

> 
> > Comments welcome.
> > 
> >  drivers/input/joystick/Kconfig    |    8 +
> >  drivers/input/joystick/Makefile   |    1 
> >  drivers/input/joystick/wiichuck.c |  225 +++++++++++++++++++++++++++++++++++++
> >  3 files changed, 234 insertions(+), 0 deletions(-)
> >  create mode 100644 drivers/input/joystick/wiichuck.c
> > 
> > diff --git a/drivers/input/joystick/Kconfig b/drivers/input/joystick/Kconfig
> > index 56eb471..79f18db 100644
> > --- a/drivers/input/joystick/Kconfig
> > +++ b/drivers/input/joystick/Kconfig
> > @@ -193,6 +193,14 @@ config JOYSTICK_TWIDJOY
> >  	  To compile this driver as a module, choose M here: the
> >  	  module will be called twidjoy.
> >  
> > +config JOYSTICK_WIICHUCK
> > +	tristate "Nintendo Nunchuck on i2c bus"
> > +	depends on I2C
> > +	select INPUT_POLLDEV
> > +	help
> > +	  Say Y here if you have a Nintendo Nunchuck directly attached to
> > +	  the machine's i2c bus.
> > +
> 
> 	To compile this driver as a module, ...

That ends up being pretty useless boilerplate.  I've stopped adding
that line to any of the Kconfig text I maintain.

> > +static void wiichuck_poll(struct input_polled_dev *poll_dev)
> > +{
> > +	struct wiichuck_device *wiichuck = poll_dev->private;
> > +	struct i2c_client *i2c = wiichuck->i2c_client;
> > +	static uint8_t cmd_byte = 0;
> > +	struct i2c_msg cmd_msg =
> > +		{ .addr = i2c->addr, .len = 1, .buf = &cmd_byte };
> > +	uint8_t b[6];
> 
> As mentioned by others these buffers should not be on stack.

Fixed.

> 
> > +	struct i2c_msg data_msg =
> > +		{ .addr = i2c->addr, .flags = I2C_M_RD, .len = 6, .buf = b };
> > +	int jx, jy, ax, ay, az;
> > +	bool c, z;
> > +
> > +	switch (wiichuck->state) {
> > +	case 0:
> > +		i2c_transfer(i2c->adapter, &cmd_msg, 1);
> > +		wiichuck->state = 1;
> 
> Do you really need to have a state machine here? Why not do both
> transfers in one poll invocation?

Mostly because there needs to a gap between setting up the data
capture and reading the data back.  I could flip things around to
setup the next transfer after reading the previous, but in my current
version I also add state for handling hotplug of the wiimote
accessories, so I think the state machine is still warranted.

> > +	set_bit(EV_KEY, input_dev->evbit);
> > +	set_bit(BTN_C, input_dev->keybit); /* buttons */
> > +	set_bit(BTN_Z, input_dev->keybit);
> 
> I prefer __set_bit() here since there is no concurrency.

In general, I avoid using __* versions of functions unless it is
actually important that I do so.  I'm not concerned about slightly
higher overhead here, and I'd rather my code set a good example.

g.
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