Subject: [PATCH 2/3 V2] iio: mxs: Implement support for touchscreen

From: [email-masked] (Marek Vasut)
Date: Thu, 10 Jan 2013 10:48:37 +0100

Dear Dmitry Torokhov,

[...]
> > > +	enum mxs_lradc_ts	use_touchscreen;
> > > +	unsigned int		stop_touchscreen:1;
> > > +	unsigned int		use_touchbutton:1;
> 
> Can we make them bools instead of bit fields?

Sure.
[...]

> > > +static void mxs_lradc_ts_close(struct input_dev *dev)
> > > +{
> > > +	struct mxs_lradc *lradc = input_get_drvdata(dev);
> > > +
> > > +	/* Indicate the touchscreen is stopping. */
> > > +	lradc->stop_touchscreen = 1;
> > > +
> > > +	/* Disable touchscreen touch-detect IRQ. */
> > > +	writel(LRADC_CTRL1_TOUCH_DETECT_IRQ_EN,
> > > +		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_CLR);
> > > +
> > > +	/* Power-down touchscreen touch-detect circuitry. */
> > > +	writel(LRADC_CTRL0_TOUCH_DETECT_ENABLE,
> > > +		lradc->base + LRADC_CTRL0 + STMP_OFFSET_REG_CLR);
> 
> These 2 writes are racing with writes in mxs_lradc_ts_work(). I think
> you need to:
> 
> 	lradc->stop_touchscreen = true;
> 	mb();

Nice catch, do we need the memory barrier here though, is it not enough to 
reorder the cancel_work_sync() just before the register writes?

> 	cancel_work_sync(&lradc->ts_work);
> 	writel(LRADC_CTRL1_TOUCH_DETECT_IRQ_EN,
> 		lradc->base + LRADC_CTRL1 + STMP_OFFSET_REG_CLR);
> 	...

[...]

> > > +	lradc->ts_input = input;
> > > +	input_set_drvdata(input, lradc);
> > > +	ret = input_register_device(input);
> > > +	if (ret)
> > > +		input_free_device(lradc->ts_input);
> > > +
> > > +	return ret;
> 
> So why is allocation failure is not fatal bur registration is? I'd make
> both fatal.

Since it's still possible to operate the block even if touchscreen fails to 
probe. If that happens, certainly something is already weird. I'd say both 
should be fatal.

> > > +}
> > > +
> > > +static void mxs_lradc_ts_unregister(struct mxs_lradc *lradc)
> > > +{
> > > +	if (!lradc->use_touchscreen)
> > > +		return;
> > > +
> > > +	if (!lradc->ts_input)
> > > +		return;
> 
> Do we really need to check both conditions?

Better safe than sorry, but lradc->ts_input should be non-NULL in case lradc-
>use_touchscreen is set, so I'll remove it.

[...]