linux-kernel - Re: [PATCH] Input: add support for the Samsung S6SY761 touchscreen

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Date:   Fri, 22 Sep 2017 10:14:10 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Andi Shyti <andi.shyti@...sung.com>
Cc:     Rob Herring <robh+dt@...nel.org>, linux-input@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andi Shyti <andi@...zian.org>
Subject: Re: [PATCH] Input: add support for the Samsung S6SY761 touchscreen

Hi Andi,

On Fri, Sep 22, 2017 at 01:17:02PM +0900, Andi Shyti wrote:
> Hi Dmitry,
> 
> thanks for your review!
> 
> [...]
> 
> > > +static void s6sy761_report_coordinates(struct s6sy761_data *sdata, u8 *event)
> > > +{
> > > +	u8 tid = ((event[0] & S6SY761_MASK_TID) >> 2) - 1;
> > 
> > Should we make sure that event[0] & S6SY761_MASK_TID is not 0?
> 
> I check event[0] already in s6sy761_handle_events (called by the
> irq handler), if we get here event[0] is for sure positive...
> 
> [...]
> 
> > > +static void s6sy761_handle_events(struct s6sy761_data *sdata, u8 left_event)
> > > +{
> > > +	int i;
> > > +
> > > +	for (i = 0; i < left_event; i++) {
> > > +		u8 *event = &sdata->data[i * S6SY761_EVENT_SIZE];
> > > +		u8 event_id = event[0] & S6SY761_MASK_EID;
> > > +
> > > +		if (!event[0])
> > > +			return;
> 		   ^^^^^^^^
> ... exactly here.
> 
> '!event[0]' means also to me that there is nothing left,
> therefore I can discard whatever is next (given that there is
> something left).

What happens if you get event[0] == S6SY761_EVENT_ID_COORDINATE? I.e.
the value is non-zero, but tid component is 0?

> 
> > > +		switch (event_id) {
> > > +
> > > +		case S6SY761_EVENT_ID_COORDINATE:
> > > +			s6sy761_handle_coordinates(sdata, event);
> > > +			break;
> > > +
> > > +		case S6SY761_EVENT_ID_STATUS:
> > > +			break;
> > > +
> > > +		default:
> > > +			break;
> > > +		}
> > > +	}
> > > +}
> 
> [...]
> 
> > > +static ssize_t s6sy761_sysfs_low_power_store(struct device *dev,
> > > +					struct device_attribute *attr,
> > > +					const char *buf, size_t len)
> > > +{
> > > +	struct s6sy761_data *sdata = dev_get_drvdata(dev);
> > > +	unsigned long value;
> > > +	s32 ret;
> > > +	u8 new_status;
> > > +
> > > +	if (kstrtoul(buf, 0, &value))
> > > +		return -EINVAL;
> > > +
> > > +	/*
> > > +	 * The device does not respond to read/write in low power,
> > > +	 * it will enable only in case of external events (e.g. touch).
> > > +	 * The i2c read will fail as expected if no external events occur
> > > +	 */
> > 
> > I am not quite sure how to parse this. Are you saying that the device in
> > low power mode will wake up when touched? Then your runtime PM
> > implementation seems incomplete.
> 
> I was startled as well when I saw this working. It cannot be in
> the PM runtime because the device would freeze (unless is
> touched). I don't know if it's a bug in the firmware or this is
> how it meant to be.
> 
> > In any case, I'd rather we did not expose this state as a custom
> > attribute.
> 
> I can remove it completely, indeed I don't see much use of it.

Great!

> 
> [...]
> 
> > > +	sdata->devid = buffer[1] << 8 | buffer[2];
> > 
> > 	get_unaligned_be16()?
> 
> Thanks!
> 
> [...]
> 
> > > +	/* check if both max_x and max_y have a value */
> > > +	if (unlikely(!sdata->prop.max_x || !sdata->prop.max_y))
> > 
> > This is not in hot path, we do not need unlikely() here.
> 
> OK, Thanks!
> 
> > > +		return -EINVAL;
> > > +
> > > +	/* if no tx channels defined, at least keep one */
> > > +	sdata->tx_channel = !buffer[8] ? 1 : buffer[8];
> > 
> > 	sdata->tx_channel = max(buffer[8], 1);
> 
> Thanks!
> 
> [...]
> 
> > > +static int s6sy761_probe(struct i2c_client *client,
> > > +			const struct i2c_device_id *id)
> > > +{
> 
> [...]
> 
> > > +	err = devm_request_threaded_irq(&client->dev, client->irq, NULL,
> > > +					s6sy761_irq_handler,
> > > +					IRQF_TRIGGER_LOW | IRQF_ONESHOT,
> > > +					"s6sy761_irq", sdata);
> > > +	if (err)
> > > +		return err;
> > > +
> > > +	disable_irq(client->irq);
> > 
> > Can you request IRQ after allocating and setting up the input device?
> > Then you do not need to check for its presence in the interrupt handler.
> 
> The reason I do it here is because the x and y are embedded in
> the device itself. This means that I first need to enable the
> device, read x and y and then register the input device.
> 
> At power up I might expect an interrupt coming, thus I need to
> check if 'input' is not 'NULL'.

But you do not need interrupts to read x and y, right? So you can power
device, create input device, set it up as needed, and then request irq,
or am I missing something?

Thanks.

-- 
Dmitry