Re: [PATCH v2 5/7] input: goldfish: Fix multitouch event handling

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Wed, Jun 28, 2017 at 05:56:29PM +0200, Aleksandar Markovic wrote:
> From: Lingfeng Yang <lfy@google.com>
> 
> Register Goldfish Events device properly as a multitouch device,
> and send SYN_REPORT event in appropriate cases only.
> 
> If SYN_REPORT is sent on every single multitouch event, it breaks
> the multitouch. The multitouch becomes janky and having to click
> 2-3 times to do stuff (plus randomly activating notification bars
> when not clicking).

This sounds like a deficiency in protocol handling in userspace. Given
that input core can suppress duplicate events userpsace mught very well
only see one ABS_X followed by SYN_REPORT if Y coordinate did not change
or was suppressed by jitter detection.

> If these SYN_REPORT events are supressed,
> multitouch will work fine, plus the events will have a protocol
> that looks nice.
> 
> In addition, Goldfish Events device needs to be registerd as a
> multitouch device by issuing input_mt_init_slots. Otherwise,
> input_handle_abs_event in drivers/input/input.c will silently drop
> all ABS_MT_SLOT events, casusing touches with more than one finger
> not to work properly.
> 
> Signed-off-by: Lingfeng Yang <lfy@google.com>
> Signed-off-by: Miodrag Dinic <miodrag.dinic@imgtec.com>
> Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com>
> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
> ---
>  drivers/input/keyboard/goldfish_events.c | 33 +++++++++++++++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/input/keyboard/goldfish_events.c b/drivers/input/keyboard/goldfish_events.c
> index f6e643b..6e0b8bb 100644
> --- a/drivers/input/keyboard/goldfish_events.c
> +++ b/drivers/input/keyboard/goldfish_events.c
> @@ -17,6 +17,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/types.h>
>  #include <linux/input.h>
> +#include <linux/input/mt.h>
>  #include <linux/kernel.h>
>  #include <linux/platform_device.h>
>  #include <linux/slab.h>
> @@ -24,6 +25,8 @@
>  #include <linux/io.h>
>  #include <linux/acpi.h>
>  
> +#define GOLDFISH_MAX_FINGERS 5
> +
>  enum {
>  	REG_READ        = 0x00,
>  	REG_SET_PAGE    = 0x00,
> @@ -52,7 +55,22 @@ static irqreturn_t events_interrupt(int irq, void *dev_id)
>  	value = __raw_readl(edev->addr + REG_READ);
>  
>  	input_event(edev->input, type, code, value);
> -	input_sync(edev->input);
> +
> +	/*
> +	 * Send an extra (EV_SYN, SYN_REPORT, 0x0) event if a key
> +	 * was pressed. Some keyboard device drivers may only send
> +	 * the EV_KEY event and not EV_SYN.

Can they be fixed?

> +	 *
> +	 * Note that sending an extra SYN_REPORT is not necessary
> +	 * nor correct protocol with other devices such as
> +	 * touchscreens, which will send their own SYN_REPORT's
> +	 * when sufficient event information has been collected
> +	 * (e.g., for touchscreens, when pressure and X/Y coordinates
> +	 * have been received). Hence, we will only send this extra
> +	 * SYN_REPORT if type == EV_KEY.
> +	 */
> +	if (type == EV_KEY)
> +		input_sync(edev->input);

Ideally we would not be sending synthetic EV_SYN at all...

>  	return IRQ_HANDLED;
>  }
>  
> @@ -155,6 +173,19 @@ static int events_probe(struct platform_device *pdev)
>  	input_dev->name = edev->name;
>  	input_dev->id.bustype = BUS_HOST;
>  
> +	/*
> +	 * Set the Goldfish Device to be multitouch.
> +	 *
> +	 * In the Ranchu kernel, there is multitouch-specific code
> +	 * for handling ABS_MT_SLOT events (see
> +	 * drivers/input/input.c:input_handle_abs_event).
> +	 * If we do not issue input_mt_init_slots, the kernel will
> +	 * filter out needed ABS_MT_SLOT events when we touch the
> +	 * screen in more than one place, preventing multitouch with
> +	 * more than one finger from working.
> +	 */
> +	input_mt_init_slots(input_dev, GOLDFISH_MAX_FINGERS, 0);

This needs error handling. Also, can the backend communicate number of
slots so the userspace has better idea about the capabilities of the
device?

> +
>  	events_import_bits(edev, input_dev->evbit, EV_SYN, EV_MAX);
>  	events_import_bits(edev, input_dev->keybit, EV_KEY, KEY_MAX);
>  	events_import_bits(edev, input_dev->relbit, EV_REL, REL_MAX);
> -- 
> 2.7.4
> 

Thanks.

-- 
Dmitry