Support brightness control on Linux fbdev

src/dev/posix/hasp_posix.cpp

@@ -25,6 +25,7 @@
 #include "display/fbdev.h"
 #endif
 
+#include <fstream>
 #include <unistd.h>
 
 // extern monitor_t monitor;
@@ -153,7 +154,31 @@ void PosixDevice::update_backlight()
 #if USE_MONITOR
     monitor_backlight(level);
 #elif USE_FBDEV
-        // set display backlight, if possible
+    // set display backlight, if possible
+    if(backlight_device != "") {
+        if(backlight_max == 0) {
+            std::ifstream f;
+            f.open("/sys/class/backlight/" + backlight_device + "/max_brightness");
+            if(!f.fail()) {
+                f >> backlight_max;
+                f.close();
+            } else {
+                perror("Max brightness read failed");
+            }
+        }
+
+        int brightness = map(level, 0, 255, 0, backlight_max);
+        LOG_VERBOSE(0, "Setting brightness to %d/255 (%d)", level, brightness);
+
+        std::ofstream f;
+        f.open("/sys/class/backlight/" + backlight_device + "/brightness");
+        if(!f.fail()) {
+            f << brightness;
+            f.close();
+        } else {
+            perror("Brightness write failed");
+        }
+    }
 #endif
 }
 

src/dev/posix/hasp_posix.h

@@ -56,6 +56,10 @@ class PosixDevice : public BaseDevice {
 
     bool is_system_pin(uint8_t pin) override;
 
+  public:
+    std::string backlight_device;
+    int backlight_max = 0;
+
   private:
     std::string _hostname;
     std::string _core_version;

src/main_pc.cpp

@@ -119,6 +119,10 @@ void usage(const char* progName, const char* version)
               << "                        (default: 'AppData\\hasp\\hasp')" << std::endl
 #elif defined(POSIX)
               << "                        (default: '~/.local/share/hasp/hasp')" << std::endl
+#endif
+#if USE_FBDEV && defined(POSIX)
+              << "    -b  | --backlight   Backlight device name (in /sys/class/backlight/)" << std::endl
+              << "    -B  | --bl-max      Backlight brightness limit (default: max_brightness)" << std::endl
 #endif
               << std::endl;
     fflush(stdout);
@@ -138,6 +142,25 @@ int main(int argc, char* argv[])
     for(int arg = 1; arg < argc; arg++) {
         if(strncmp(argv[arg], "--help", 6) == 0 || strncmp(argv[arg], "-h", 2) == 0) {
             showhelp = true;
+#if USE_FBDEV && defined(POSIX)
+        } else if(strncmp(argv[arg], "--backlight", 11) == 0 || strncmp(argv[arg], "-b", 2) == 0) {
+            if(arg + 1 < argc) {
+                haspDevice.backlight_device = argv[arg + 1];
+                arg++;
+            } else {
+                std::cout << "Missing device name" << std::endl;
+                showhelp = true;
+            }
+        } else if(strncmp(argv[arg], "--bl-max", 9) == 0 || strncmp(argv[arg], "-B", 2) == 0) {
+            if(arg + 1 < argc) {
+                int bl_max = atoi(argv[arg + 1]);
+                if(bl_max > 0) haspDevice.backlight_max = bl_max;
+                arg++;
+            } else {
+                std::cout << "Missing backlight level" << std::endl;
+                showhelp = true;
+            }
+#endif
         } else if(strncmp(argv[arg], "--width", 7) == 0 || strncmp(argv[arg], "-W", 2) == 0) {
             if(arg + 1 < argc) {
                 int w = atoi(argv[arg + 1]);