linux-kernel - [PATCH] input: goldfish: Fix multitouch event handling

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Date:   Fri, 25 Aug 2017 15:40:16 +0200
From:   Aleksandar Markovic <aleksandar.markovic@...rk.com>
To:     linux-kernel@...r.kernel.org, linux-input@...r.kernel.org
Cc:     goran.ferenc@...tec.com, aleksandar.markovic@...tec.com,
        miodrag.dinic@...tec.com, petar.jovanovic@...tec.com,
        raghu.gandham@...tec.com, dmitry.torokhov@...il.com,
        alan@...ux.intel.com, jinqian@...roid.com, sheng@...ux.intel.com,
        lfy@...gle.com
Subject: [PATCH] input: goldfish: Fix multitouch event handling

From: Lingfeng Yang <lfy@...gle.com>

Register Goldfish Events device properly as a multitouch device, and
send SYN_REPORT events in appropriate cases only.

If SYN_REPORT event is sent on every single multitouch event, it
breaks the multitouch support. The multitouch interaction becomes
janky and user has to click 2-3 times to do stuff (also, notification
bars are randomly activating when not clicking). If these SYN_REPORT
events are suppressed, like it is done after this patch iss applied,
multitouch works fine, plus the events have a protocol that looks
nice.

In addition, Goldfish Events device needs to be registered as a
multitouch device by issuing input_mt_init_slots. Otherwise, function
input_handle_abs_event in drivers/input/input.c will silently drop all
ABS_MT_SLOT events, causing touches with more than one finger not to
work properly.

Signed-off-by: Lingfeng Yang <lfy@...gle.com>
Signed-off-by: Miodrag Dinic <miodrag.dinic@...tec.com>
Signed-off-by: Goran Ferenc <goran.ferenc@...tec.com>
Signed-off-by: Aleksandar Markovic <aleksandar.markovic@...tec.com>
---
 drivers/input/keyboard/goldfish_events.c | 35 +++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/drivers/input/keyboard/goldfish_events.c b/drivers/input/keyboard/goldfish_events.c
index f6e643b..bc3e8b3 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 only if a key
+	 * was pressed. Some keyboard device drivers may only send the
+	 * EV_KEY event and not the EV_SYN event.
+	 *
+	 * 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_REPORTs when sufficient event
+	 * event information has been collected (for example, in case
+	 * 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);
 	return IRQ_HANDLED;
 }
 
@@ -155,6 +173,21 @@ 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 file drivers/input/input.c,
+	 * function 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.
+	 */
+	error = input_mt_init_slots(input_dev, GOLDFISH_MAX_FINGERS, 0);
+	if (error)
+		return error;
+
 	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);
-- 
2.9.3