Kobo: Only probe necessary entries in automagic_sysfs codepath

e.g., on the Sage, only the power_dev stuff changes between HW revs,
the rest of the hardcoded stuff is still relevant, so skip probing
those.

frontend/device/kobo/device.lua

@@ -627,57 +627,69 @@ function Kobo:init()
     -- Automagic sysfs discovery
     if self.automagic_sysfs then
         -- Battery
-        if util.pathExists("/sys/class/power_supply/battery") then
-            -- Newer devices (circa sunxi)
-            self.battery_sysfs = "/sys/class/power_supply/battery"
-        else
-            self.battery_sysfs = "/sys/class/power_supply/mc13892_bat"
+        if not self.battery_sysfs then
+            if util.pathExists("/sys/class/power_supply/battery") then
+                -- Newer devices (circa sunxi)
+                self.battery_sysfs = "/sys/class/power_supply/battery"
+            else
+                self.battery_sysfs = "/sys/class/power_supply/mc13892_bat"
+            end
         end
 
         -- Frontlight
         if self:hasNaturalLight() then
-            if util.fileExists("/sys/class/leds/aw99703-bl_FL1/color") then
-                -- HWConfig FL_PWM is AW99703x2
-                self.frontlight_settings.frontlight_mixer = "/sys/class/leds/aw99703-bl_FL1/color"
-            elseif util.fileExists("/sys/class/backlight/lm3630a_led/color") then
-                -- HWConfig FL_PWM is LM3630
-                self.frontlight_settings.frontlight_mixer = "/sys/class/backlight/lm3630a_led/color"
-            elseif util.fileExists("/sys/class/backlight/tlc5947_bl/color") then
-                -- HWConfig FL_PWM is TLC5947
-                self.frontlight_settings.frontlight_mixer = "/sys/class/backlight/tlc5947_bl/color"
+            if not self.frontlight_settings.frontlight_mixer then
+                if util.fileExists("/sys/class/leds/aw99703-bl_FL1/color") then
+                    -- HWConfig FL_PWM is AW99703x2
+                    self.frontlight_settings.frontlight_mixer = "/sys/class/leds/aw99703-bl_FL1/color"
+                elseif util.fileExists("/sys/class/backlight/lm3630a_led/color") then
+                    -- HWConfig FL_PWM is LM3630
+                    self.frontlight_settings.frontlight_mixer = "/sys/class/backlight/lm3630a_led/color"
+                elseif util.fileExists("/sys/class/backlight/tlc5947_bl/color") then
+                    -- HWConfig FL_PWM is TLC5947
+                    self.frontlight_settings.frontlight_mixer = "/sys/class/backlight/tlc5947_bl/color"
+                end
             end
         end
 
-        -- Input
-        if util.fileExists("/dev/input/by-path/platform-1-0010-event") then
-            -- Elan (HWConfig TouchCtrl is ekth6) on i2c bus 1
-            self.touch_dev = "/dev/input/by-path/platform-1-0010-event"
-        elseif util.fileExists("/dev/input/by-path/platform-0-0010-event") then
-            -- Elan (HWConfig TouchCtrl is ekth6) on i2c bus 0
-            self.touch_dev = "/dev/input/by-path/platform-0-0010-event"
-        else
-            self.touch_dev = "/dev/input/event1"
+        -- Touch panel input
+        if not self.touch_dev then
+            if util.fileExists("/dev/input/by-path/platform-1-0010-event") then
+                -- Elan (HWConfig TouchCtrl is ekth6) on i2c bus 1
+                self.touch_dev = "/dev/input/by-path/platform-1-0010-event"
+            elseif util.fileExists("/dev/input/by-path/platform-0-0010-event") then
+                -- Elan (HWConfig TouchCtrl is ekth6) on i2c bus 0
+                self.touch_dev = "/dev/input/by-path/platform-0-0010-event"
+            else
+                self.touch_dev = "/dev/input/event1"
+            end
         end
 
-        if util.fileExists("/dev/input/by-path/platform-gpio-keys-event") then
-            -- Libra 2 w/ a BD71828 PMIC
-            self.ntx_dev = "/dev/input/by-path/platform-gpio-keys-event"
-        elseif util.fileExists("/dev/input/by-path/platform-ntx_event0-event") then
-            -- sunxi & Mk. 7
-            self.ntx_dev = "/dev/input/by-path/platform-ntx_event0-event"
-        elseif util.fileExists("/dev/input/by-path/platform-mxckpd-event") then
-            -- circa Mk. 5 i.MX
-            self.ntx_dev = "/dev/input/by-path/platform-mxckpd-event"
-        else
-            self.ntx_dev = "/dev/input/event0"
+        -- Physical buttons & synthetic NTX events
+        if not self.ntx_dev then
+            if util.fileExists("/dev/input/by-path/platform-gpio-keys-event") then
+                -- Libra 2 w/ a BD71828 PMIC
+                self.ntx_dev = "/dev/input/by-path/platform-gpio-keys-event"
+            elseif util.fileExists("/dev/input/by-path/platform-ntx_event0-event") then
+                -- sunxi & Mk. 7
+                self.ntx_dev = "/dev/input/by-path/platform-ntx_event0-event"
+            elseif util.fileExists("/dev/input/by-path/platform-mxckpd-event") then
+                -- circa Mk. 5 i.MX
+                self.ntx_dev = "/dev/input/by-path/platform-mxckpd-event"
+            else
+                self.ntx_dev = "/dev/input/event0"
+            end
         end
 
-        if util.fileExists("/dev/input/by-path/platform-bd71828-pwrkey-event") then
-            -- Libra 2 w/ a BD71828 PMIC
-            self.power_dev = "/dev/input/by-path/platform-bd71828-pwrkey-event"
-        elseif util.fileExists("/dev/input/by-path/platform-bd71828-pwrkey.4.auto-event") then
-            -- Fix for Kobo Sage, presumably w/ a BD71828 PMIC?
-            self.power_dev = "/dev/input/by-path/platform-bd71828-pwrkey.4.auto-event"
+        -- Power button (this usually ends up in ntx_dev, except with some PMICs)
+        if not self.power_dev then
+            if util.fileExists("/dev/input/by-path/platform-bd71828-pwrkey-event") then
+                -- Libra 2 w/ a BD71828 PMIC
+                self.power_dev = "/dev/input/by-path/platform-bd71828-pwrkey-event"
+            elseif util.fileExists("/dev/input/by-path/platform-bd71828-pwrkey.4.auto-event") then
+                -- Sage w/ a BD71828 PMIC
+                self.power_dev = "/dev/input/by-path/platform-bd71828-pwrkey.4.auto-event"
+            end
         end
     end