[opentitantool] Support gpio analog-write via proxy

Add a few method needed to propagate calls to `Gpio::analog_write()` and
`Gpio::analog_read()` via the proxy protocol.  This appears to have been
an oversight at the time when the analog functionality was added, which
has gone undetected the feature was needed by Google now.

Change-Id: I89b66c86a79ce4686fd3259373f7c057cffb4783
Signed-off-by: Jes B. Klinke <jbk@chromium.org>

sw/host/opentitanlib/src/proxy/handler.rs

@@ -96,6 +96,14 @@ impl<'a> TransportCommandHandler<'a> {
                         instance.set_pull_mode(*pull)?;
                         Ok(Response::Gpio(GpioResponse::SetPullMode))
                     }
+                    GpioRequest::AnalogRead => {
+                        let value = instance.analog_read()?;
+                        Ok(Response::Gpio(GpioResponse::AnalogRead { value }))
+                    }
+                    GpioRequest::AnalogWrite { value } => {
+                        instance.analog_write(*value)?;
+                        Ok(Response::Gpio(GpioResponse::AnalogWrite))
+                    }
                     GpioRequest::MultiSet {
                         mode,
                         value,

sw/host/opentitanlib/src/proxy/protocol.rs

@@ -75,6 +75,10 @@ pub enum GpioRequest {
     SetPullMode {
         pull: PullMode,
     },
+    AnalogWrite {
+        value: f32,
+    },
+    AnalogRead,
     MultiSet {
         mode: Option<PinMode>,
         value: Option<bool>,
@@ -89,6 +93,8 @@ pub enum GpioResponse {
     Read { value: bool },
     SetMode,
     SetPullMode,
+    AnalogWrite,
+    AnalogRead { value: f32 },
     MultiSet,
 }
 

sw/host/opentitanlib/src/transport/proxy/gpio.rs

@@ -76,6 +76,20 @@ impl GpioPin for ProxyGpioPin {
         }
     }
 
+    fn analog_read(&self) -> Result<f32> {
+        match self.execute_command(GpioRequest::AnalogRead)? {
+            GpioResponse::AnalogRead { value } => Ok(value),
+            _ => bail!(ProxyError::UnexpectedReply()),
+        }
+    }
+
+    fn analog_write(&self, volts: f32) -> Result<()> {
+        match self.execute_command(GpioRequest::AnalogWrite { value: volts })? {
+            GpioResponse::AnalogWrite => Ok(()),
+            _ => bail!(ProxyError::UnexpectedReply()),
+        }
+    }
+
     fn set(
         &self,
         mode: Option<PinMode>,