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SubjectRe: [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@secretlab.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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