i2c-smbus: linux: Fix interface detection

There are cases where detection of an interface fails due to lack of
permissions when accessing /dev/i2c-*. In some instances, the current
code will perform a double readdir() and skip what should have been
the next interface to be enumerated.

E.g. consider a system with the following configuration

  $ ls -l /sys/bus/i2c/devices

  total 0
  lrwxrwxrwx. 1 root 0 Sep  4 07:19 i2c-0 -> ../../../devices/platform/AMDI0010:03/i2c-0/
  lrwxrwxrwx. 1 root 0 Sep  4 01:49 i2c-1 -> ../../../devices/pci0000:00/0000:00:08.1/0000:03:00.0/i2c-1/
  lrwxrwxrwx. 1 root 0 Sep  4 01:50 i2c-10 -> ../../../devices/pci0000:00/0000:00:14.0/i2c-10/
  lrwxrwxrwx. 1 root 0 Sep  4 01:49 i2c-2 -> ../../../devices/pci0000:00/0000:00:08.1/0000:03:00.0/i2c-2/
  lrwxrwxrwx. 1 root 0 Sep  4 01:49 i2c-3 -> ../../../devices/pci0000:00/0000:00:08.1/0000:03:00.0/i2c-3/
  lrwxrwxrwx. 1 root 0 Sep  4 01:49 i2c-4 -> ../../../devices/pci0000:00/0000:00:08.1/0000:03:00.0/i2c-4/
  lrwxrwxrwx. 1 root 0 Sep  4 01:49 i2c-5 -> ../../../devices/pci0000:00/0000:00:08.1/0000:03:00.0/drm/card1/card1-eDP-1/i2c-5/
  lrwxrwxrwx. 1 root 0 Sep  4 01:49 i2c-6 -> ../../../devices/pci0000:00/0000:00:08.1/0000:03:00.0/drm/card1/card1-DP-1/i2c-6/
  lrwxrwxrwx. 1 root 0 Sep  4 01:49 i2c-7 -> ../../../devices/pci0000:00/0000:00:08.1/0000:03:00.0/drm/card1/card1-DP-2/i2c-7/
  lrwxrwxrwx. 1 root 0 Sep  4 01:50 i2c-8 -> ../../../devices/pci0000:00/0000:00:14.0/i2c-8/
  lrwxrwxrwx. 1 root 0 Sep  4 01:50 i2c-9 -> ../../../devices/pci0000:00/0000:00:14.0/i2c-9/
  lrwxrwxrwx. 1 root 0 Sep  4 07:19 i2c-PNP0C50:0e -> ../../../devices/platform/AMDI0010:03/i2c-0/i2c-PNP0C50:0e/

  $ openrgb --verbose --list-devices

Before:

  ...
  Registering I2C interface: /dev/i2c-3 Device 1002:164C Subsystem: 1462:130C
  Registering I2C interface: /dev/i2c-10 Device 1022:790B Subsystem: 1462:130C
  Registering I2C interface: /dev/i2c-1 Device 1002:164C Subsystem: 1462:130C
  Registering I2C interface: /dev/i2c-8 Device 1022:790B Subsystem: 1462:130C
  [i2c_smbus_linux] Failed to read i2c device PCI device ID
  Registering I2C interface: /dev/i2c-6 Device 0000:0000 Subsystem: 0000:0000
  Registering I2C interface: /dev/i2c-4 Device 1002:164C Subsystem: 1462:130C
  [i2c_smbus_linux] Failed to read i2c device PCI device ID
  Registering I2C interface: /dev/i2c-PNP0C50:0e Device 0000:0000 Subsystem: 0000:0000
  Registering I2C interface: /dev/i2c-0 Device 0000:0000 Subsystem: 0000:0000
  Registering I2C interface: /dev/i2c-9 Device 1022:790B Subsystem: 1462:130C
  [i2c_smbus_linux] Failed to read i2c device PCI device ID
  Registering I2C interface: /dev/i2c-7 Device 0000:0000 Subsystem: 0000:0000
  [i2c_smbus_linux] Failed to read i2c device PCI device ID
  Registering I2C interface: /dev/i2c-5 Device 0000:0000 Subsystem: 0000:0000
  ...

After:

  ...
  Registering I2C interface: /dev/i2c-3 Device 1002:164C Subsystem: 1462:130C
  Registering I2C interface: /dev/i2c-10 Device 1022:790B Subsystem: 1462:130C
  Registering I2C interface: /dev/i2c-1 Device 1002:164C Subsystem: 1462:130C
  Registering I2C interface: /dev/i2c-8 Device 1022:790B Subsystem: 1462:130C
  [i2c_smbus_linux] Failed to read i2c device PCI device ID
  Registering I2C interface: /dev/i2c-6 Device 0000:0000 Subsystem: 0000:0000
  Registering I2C interface: /dev/i2c-4 Device 1002:164C Subsystem: 1462:130C
  [i2c_smbus_linux] Failed to read i2c device PCI device ID
  Registering I2C interface: /dev/i2c-PNP0C50:0e Device 0000:0000 Subsystem: 0000:0000
  Registering I2C interface: /dev/i2c-2 Device 1002:164C Subsystem: 1462:130C
  Registering I2C interface: /dev/i2c-0 Device 0000:0000 Subsystem: 0000:0000
  Registering I2C interface: /dev/i2c-9 Device 1022:790B Subsystem: 1462:130C
  [i2c_smbus_linux] Failed to read i2c device PCI device ID
  Registering I2C interface: /dev/i2c-7 Device 0000:0000 Subsystem: 0000:0000
  [i2c_smbus_linux] Failed to read i2c device PCI device ID
  Registering I2C interface: /dev/i2c-5 Device 0000:0000 Subsystem: 0000:0000
  ...

Signed-off-by: Sandipan Das <[email protected]>

Author: sandip4n

i2c_smbus/i2c_smbus_linux.cpp

@@ -94,15 +94,7 @@ bool i2c_smbus_linux_detect()
     }
 
     // Loop through all entries in i2c-adapter list
-    ent = readdir(dir);
-
-    if(ent == NULL)
-    {
-        closedir(dir);
-        return(false);
-    }
-
-    while(ent != NULL)
+    while((ent = readdir(dir)) != NULL)
     {
         if(ent->d_type == DT_DIR || ent->d_type == DT_LNK)
         {
@@ -229,7 +221,6 @@ bool i2c_smbus_linux_detect()
 
                     if (test_fd < 0)
                     {
-                        ent = readdir(dir);
                         ret = false;
                     }
 
@@ -249,7 +240,6 @@ bool i2c_smbus_linux_detect()
                 }
             }
         }
-        ent = readdir(dir);
     }
     closedir(dir);