A few Kindle fixes (#4394)

* Implement isWifiOn on Kindle (fix #4380)
* Ensure frontlight intensity is properly restored on resume on Kindle. (fix #Fix #4392)
Only actually matters when the frontlight is *off*.

frontend/device/kindle/device.lua

@@ -16,6 +16,30 @@ local function kindleEnableWifi(toggle)
     end
 end
 
+local function isWifiUp()
+    -- NOTE: Pilfered from Cervantes, c.f., #4380
+    --       Possibly simpler and more compatible than the lipc approach ;).
+    local file = io.open("/sys/class/net/wlan0/carrier", "rb")
+    if not file then return 0 end
+    local status = tonumber(file:read("*all")) or 0
+    file:close()
+    return status
+
+    --[[
+    local status = 0
+    local haslipc, lipc = pcall(require, "liblipclua")
+    local lipc_handle = nil
+    if haslipc and lipc then
+        lipc_handle = lipc.init("com.github.koreader.networkmgr")
+    end
+    if lipc_handle then
+        status = lipc_handle:get_int_property("com.lab126.wifid", "enable")
+        lipc_handle:close()
+    end
+    return status
+    --]]
+end
+
 --[[
 Test if a kindle device has Special Offers
 --]]
@@ -62,6 +86,10 @@ function Kindle:initNetworkManager(NetworkMgr)
     NetworkMgr.turnOffWifi = function()
         kindleEnableWifi(0)
     end
+
+    NetworkMgr.isWifiOn = function()
+        return 1 == isWifiUp()
+    end
 end
 
 function Kindle:supportsScreensaver()

frontend/device/kindle/powerd.lua

@@ -21,18 +21,24 @@ function KindlePowerD:frontlightIntensityHW()
     if self.lipc_handle ~= nil then
         return self.lipc_handle:get_int_property("com.lab126.powerd", "flIntensity")
     else
+        -- NOTE: This fallback is of dubious use, as it will NOT match our expected [fl_min..fl_max] range,
+        --       each model has a specific curve.
         return self:_readFLIntensity()
     end
 end
 
 function KindlePowerD:setIntensityHW(intensity)
-    if self.lipc_handle ~= nil and intensity > 0 then
+    -- NOTE: This means we *require* a working lipc handle to set the FL:
+    --       it knows what the UI values should map to for the specific hardware much better than us.
+    if self.lipc_handle ~= nil then
         -- NOTE: We want to bypass setIntensity's shenanigans and simply restore the light as-is
         self.lipc_handle:set_int_property(
             "com.lab126.powerd", "flIntensity", intensity)
-    else
-        -- NOTE: when intensity is 0, We want to really kill the light, so do it manually
-        -- (asking lipc to set it to 0 would in fact set it to 1)...
+    end
+    if intensity == 0 then
+        -- NOTE: when intensity is 0, we want to *really* kill the light, so do it manually
+        -- (asking lipc to set it to 0 would in fact set it to 1 on most Kindles).
+        -- We do *both* to make the fl restore on resume less jarring on devices where lipc 0 != off.
         os.execute("echo -n ".. intensity .." > " .. self.fl_intensity_file)
     end
 end
@@ -70,12 +76,16 @@ function KindlePowerD:afterResume()
     if not self.device.hasFrontlight() then
         return
     end
+    local UIManager = require("ui/uimanager")
     if self:isFrontlightOn() then
-        -- Kindle stock software should turn on the front light automatically. The follow statement
-        -- ensure the consistency of intensity.
-        self:turnOnFrontlightHW()
+        -- The Kindle framework should turn the front light back on automatically.
+        -- The following statement ensures consistency of intensity, but should basically always be redundant,
+        -- since we set intensity via lipc and not sysfs ;).
+        -- NOTE: This is race-y, and we want to *lose* the race, hence the use of the scheduler (c.f., #4392)
+        UIManager:tickAfterNext(function() self:turnOnFrontlightHW() end)
     else
-        self:turnOffFrontlightHW()
+        -- But in the off case, we *do* use sysfs, so this one actually matters.
+        UIManager:tickAfterNext(function() self:turnOffFrontlightHW() end)
     end
 end
 

spec/unit/device_spec.lua

@@ -232,18 +232,20 @@ describe("device module", function()
 
             assert.is.same(kindle_dev.powerd.fl_intensity, 12)
             kindle_dev.powerd:setIntensity(5)
-            assert.stub(os.execute).was_called_with(
-                "echo -n 5 > /sys/class/backlight/max77696-bl/brightness")
             assert.is.same(kindle_dev.powerd.fl_intensity, 5)
 
             kindle_dev.powerd:toggleFrontlight()
             assert.stub(os.execute).was_called_with(
                 "echo -n 0 > /sys/class/backlight/max77696-bl/brightness")
+            -- Here be shenanigans: we don't override powerd's fl_intensity when we turn the light off,
+            -- so that we can properly turn it back on at the previous intensity ;)
             assert.is.same(kindle_dev.powerd.fl_intensity, 5)
+            -- But if we were to cat /sys/class/backlight/max77696-bl/brightness, it should now be 0.
 
             kindle_dev.powerd:toggleFrontlight()
-            assert.stub(os.execute).was_called_with(
-                "echo -n 5 > /sys/class/backlight/max77696-bl/brightness")
+            assert.is.same(kindle_dev.powerd.fl_intensity, 5)
+            -- And /sys/class/backlight/max77696-bl/brightness is now !0
+            -- (exact value is HW-dependent, each model has a different curve, we let lipc do the work for us).
         end)
 
         it("oasis should interpret orientation event", function()