Try to detect 1-register-only devices, which are designed to be

accessed with SMBus receive byte and SMBus send byte transactions
(i.e. short reads and short writes) and treat SMBus read byte as a
real write followed by a read. The device detection routines would
write random values to the chip with possibly very nasty results for
the hardware. So when we detect such a chip, we skip all probing for
this address.


git-svn-id: http://lm-sensors.org/svn/lm-sensors/trunk@5247 7894878c-1315-0410-8ee3-d5d059ff63e0

CHANGES

@@ -18,6 +18,7 @@ SVN-HEAD
                           Add Intel ICH10 (bus) detection
                           Don't probe I2C addresses 0x40-0x47
                           Fix the parsing of I2C addresses not to scan
+                          Detect and skip 1-register-only I2C devices
 
 2.10.6 "Welcome Home Lina" (20080306)
   Library: Fix fschrc and fschmd support

prog/detect/sensors-detect

@@ -2761,6 +2761,43 @@ sub i2c_probe($$$)
   }
 }
 
+# $_[0]: Reference to an opened file handle
+# Returns: 1 if the device is safe to access, 0 else.
+# This function is meant to prevent access to 1-register-only devices,
+# which are designed to be accessed with SMBus receive byte and SMBus send
+# byte transactions (i.e. short reads and short writes) and treat SMBus
+# read byte as a real write followed by a read. The device detection
+# routines would write random values to the chip with possibly very nasty
+# results for the hardware. Note that this function won't catch all such
+# chips, as it assumes that reads and writes relate to the same register,
+# but that's the best we can do.
+sub i2c_safety_check
+{
+  my ($file) = @_;
+  my $data;
+
+  # First we receive a byte from the chip, and remember it.
+  $data = i2c_smbus_read_byte($file);
+  return 1 if ($data < 0);
+
+  # We receive a byte again; very likely to be the same for
+  # 1-register-only devices.
+  return 1 if (i2c_smbus_read_byte($file) != $data);
+
+  # Then we try a standard byte read, with a register offset equal to
+  # the byte we received; we should receive the same byte value in return.
+  return 1 if (i2c_smbus_read_byte_data($file, $data) != $data);
+
+  # Then we try a standard byte read, with a slightly different register
+  # offset; we should again receive the same byte value in return.
+  return 1 if (i2c_smbus_read_byte_data($file, $data ^ 1) != ($data ^ 1));
+
+  # Apprently this is a 1-register-only device, restore the original register
+  # value and leave it alone.
+  i2c_smbus_read_byte_data($file, $data);
+  return 0;
+}
+
 ####################
 # ADAPTER SCANNING #
 ####################
@@ -3107,6 +3144,10 @@ sub scan_adapter
 
     next unless i2c_probe(\*FILE, $addr, $funcs);
     printf "Client found at address 0x%02x\n",$addr;
+    if (!i2c_safety_check(\*FILE)) {
+      print "Seems to be a 1-register-only device, skipping.\n";
+      next;
+    }
 
     $| = 1;
     foreach $chip (@chip_ids) {