Fix for PR #7415 breaking reMarkable touch input (#7536)

The Wacom pen reports sane CLOCK_REALTIME timestamps, but the Touchscreen reports timestamps frozen at the boot time ts (in REALTIME) :s.

So, make everyone use synthetic CLOCK_MONOTONIC timestamps in order to make gesture detection behave.

frontend/device/remarkable/device.lua

@@ -1,5 +1,9 @@
 local Generic = require("device/generic/device") -- <= look at this file!
+local TimeVal = require("ui/timeval")
 local logger = require("logger")
+local ffi = require("ffi")
+local C = ffi.C
+require("ffi/linux_input_h")
 
 local function yes() return true end
 local function no() return false end
@@ -15,11 +19,6 @@ local function getModel()
     return model == "reMarkable 2.0", model
 end
 
-local EV_ABS = 3
-local ABS_X = 00
-local ABS_Y = 01
-local ABS_MT_POSITION_X = 53
-local ABS_MT_POSITION_Y = 54
 -- Resolutions from libremarkable src/framebuffer/common.rs
 local screen_width = 1404 -- unscaled_size_check: ignore
 local screen_height = 1872 -- unscaled_size_check: ignore
@@ -56,13 +55,13 @@ local Remarkable1 = Remarkable:new{
 }
 
 function Remarkable1:adjustTouchEvent(ev, by)
-    if ev.type == EV_ABS then
+    if ev.type == C.EV_ABS then
         -- Mirror X and Y and scale up both X & Y as touch input is different res from
         -- display
-        if ev.code == ABS_MT_POSITION_X then
+        if ev.code == C.ABS_MT_POSITION_X then
             ev.value = (Remarkable1.mt_width - ev.value) *  by.mt_scale_x
         end
-        if ev.code == ABS_MT_POSITION_Y then
+        if ev.code == C.ABS_MT_POSITION_Y then
             ev.value = (Remarkable1.mt_height - ev.value) * by.mt_scale_y
         end
     end
@@ -79,25 +78,32 @@ local Remarkable2 = Remarkable:new{
 }
 
 function Remarkable2:adjustTouchEvent(ev, by)
-    if ev.type == EV_ABS then
+    if ev.type == C.EV_ABS then
         -- Mirror Y and scale up both X & Y as touch input is different res from
         -- display
-        if ev.code == ABS_MT_POSITION_X then
+        if ev.code == C.ABS_MT_POSITION_X then
             ev.value = (ev.value) * by.mt_scale_x
         end
-        if ev.code == ABS_MT_POSITION_Y then
+        if ev.code == C.ABS_MT_POSITION_Y then
             ev.value = (Remarkable2.mt_height - ev.value) * by.mt_scale_y
         end
     end
+
+    -- Wacom uses CLOCK_REALTIME, but the Touchscreen spits out frozen timestamps.
+    -- Inject CLOCK_MONOTONIC timestamps at the end of every input frame in order to have consistent gesture detection across input devices.
+    -- c.f., #7536
+    if ev.type == C.EV_SYN and ev.code == C.SYN_REPORT then
+       ev.time = TimeVal:now()
+    end
 end
 
 local adjustAbsEvt = function(self, ev)
-    if ev.type == EV_ABS then
-        if ev.code == ABS_X then
-            ev.code = ABS_Y
+    if ev.type == C.EV_ABS then
+        if ev.code == C.ABS_X then
+            ev.code = C.ABS_Y
             ev.value = (wacom_height - ev.value) * wacom_scale_y
-        elseif ev.code == ABS_Y then
-            ev.code = ABS_X
+        elseif ev.code == C.ABS_Y then
+            ev.code = C.ABS_X
             ev.value = ev.value * wacom_scale_x
         end
     end