[i2c] Remove the "func" argument from funcs()

The funcs() implementation is buggy as it doesn't take "func" by
reference and it only defaults to SMBUS and hence the I2C protocol is
never chosen as a function.

Since the value of "func" is never required to be set by the caller, it
shouldn't be passed as argument in the first place. Make the function
return Result<u64> instead.

The test test_funcs() was failing before this change and passes after
it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

src/i2c/src/i2c.rs

@@ -264,7 +264,7 @@ pub trait I2cDevice {
         Self: Sized;
 
     // Corresponds to the I2C_FUNCS ioctl call.
-    fn funcs(&mut self, func: u64) -> Result<()>;
+    fn funcs(&mut self) -> Result<u64>;
 
     // Corresponds to the I2C_RDWR ioctl call.
     fn rdwr(&self, data: &I2cRdwrIoctlData) -> Result<()>;
@@ -299,13 +299,17 @@ impl I2cDevice for PhysDevice {
         })
     }
 
-    fn funcs(&mut self, func: u64) -> Result<()> {
-        let ret = unsafe { ioctl(self.file.as_raw_fd(), I2C_FUNCS, &func) };
+    fn funcs(&mut self) -> Result<u64> {
+        let mut func: u64 = 0;
+
+        // Safe as the file is a valid I2C adapter, the kernel will only
+        // update the correct amount of memory in func.
+        let ret = unsafe { ioctl(self.file.as_raw_fd(), I2C_FUNCS, &mut func) };
 
         if ret == -1 {
             Err(Error::IoctlFailure("funcs", IoError::last()))
         } else {
-            Ok(())
+            Ok(func)
         }
     }
 
@@ -353,11 +357,9 @@ pub struct I2cAdapter<D: I2cDevice> {
 impl<D: I2cDevice> I2cAdapter<D> {
     // Creates a new adapter corresponding to `device`.
     fn new(mut device: D) -> Result<I2cAdapter<D>> {
-        let func: u64 = I2C_FUNC_SMBUS_ALL;
-
-        device.funcs(func)?;
-
         let smbus;
+
+        let func = device.funcs()?;
         if (func & I2C_FUNC_I2C) != 0 {
             smbus = false;
         } else if (func & I2C_FUNC_SMBUS_ALL) != 0 {
@@ -510,13 +512,25 @@ pub mod tests {
 
     #[derive(Debug)]
     pub struct DummyDevice {
-        funcs_result: Result<()>,
+        funcs_result: Result<u64>,
         rdwr_result: Result<()>,
         smbus_result: Result<()>,
         slave_result: Result<()>,
         adapter_no: u32,
     }
 
+    impl Default for DummyDevice {
+        fn default() -> Self {
+            Self {
+                funcs_result: Ok(I2C_FUNC_I2C),
+                rdwr_result: Ok(()),
+                smbus_result: Ok(()),
+                slave_result: Ok(()),
+                adapter_no: 0,
+            }
+        }
+    }
+
     impl I2cDevice for DummyDevice {
         fn open(adapter_no: u32) -> Result<Self>
         where
@@ -524,14 +538,11 @@ pub mod tests {
         {
             Ok(DummyDevice {
                 adapter_no,
-                funcs_result: Ok(()),
-                rdwr_result: Ok(()),
-                smbus_result: Ok(()),
-                slave_result: Ok(()),
+                ..Default::default()
             })
         }
 
-        fn funcs(&mut self, _func: u64) -> Result<()> {
+        fn funcs(&mut self) -> Result<u64> {
             self.funcs_result
         }
 
@@ -555,14 +566,14 @@ pub mod tests {
     #[test]
     fn test_funcs() {
         let i2c_device = DummyDevice {
-            funcs_result: I2C_FUNC_SMBUS_ALL as i32,
+            funcs_result: Ok(I2C_FUNC_SMBUS_ALL),
             ..Default::default()
         };
         let adapter = I2cAdapter::new(i2c_device).unwrap();
         assert_eq!(adapter.smbus, true);
 
         let i2c_device = DummyDevice {
-            funcs_result: I2C_FUNC_I2C as i32,
+            funcs_result: Ok(I2C_FUNC_I2C),
             ..Default::default()
         };
         let adapter = I2cAdapter::new(i2c_device).unwrap();