[opentitanlib,qemu] Implement a minimal USB host

This virtual host talks to the QEMU usbdev driver. At the moment,
this host perform the initial handshake, turns on vbus, waits for
a device connection and retrieve the device descriptor.

Signed-off-by: Amaury Pouly <[email protected]>

Author: pamaury

sw/host/opentitanlib/src/transport/qemu/mod.rs

@@ -34,7 +34,7 @@ use crate::transport::qemu::monitor::{Chardev, ChardevKind, Monitor};
 use crate::transport::qemu::reset::QemuReset;
 use crate::transport::qemu::spi::QemuSpi;
 use crate::transport::qemu::uart::QemuUart;
-use crate::transport::qemu::usbdev::QemuVbusSense;
+use crate::transport::qemu::usbdev::{QemuUsbHost, QemuVbusSense};
 use crate::transport::{
     Capabilities, Capability, Transport, TransportError, TransportInterfaceType,
 };
@@ -73,6 +73,8 @@ pub struct Qemu {
     /// VBUS sense pin (actually goes via the `usbdev-cmd` chardev).
     vbus_sense: Option<Rc<dyn GpioPin>>,
 
+    _usb_host: Option<Rc<QemuUsbHost>>,
+
     /// QEMU log modelled as a UART.
     log: Option<Rc<dyn Uart>>,
 
@@ -152,6 +154,25 @@ impl Qemu {
             }
         };
 
+        // USBDEV host:
+        let usb_host = match find_chardev(&chardevs, "usbdev-host") {
+            Some(ChardevKind::Pty { path }) => {
+                let tty = serialport::new(
+                    path.to_str().context("TTY path not UTF8")?,
+                    CONSOLE_BAUDRATE,
+                )
+                .open_native()
+                .context("failed to open QEMU usbdev-host PTY")?;
+
+                let usb_host = Rc::new(QemuUsbHost::new(tty));
+                Some(usb_host)
+            }
+            _ => {
+                log::info!("could not find pty chardev with id=usbdev-host, skipping USBDEV");
+                None
+            }
+        };
+
         // QEMU log, not really a UART but modelled as one:
         let log = match find_chardev(&chardevs, "log") {
             Some(ChardevKind::Pty { path }) => {
@@ -237,6 +258,7 @@ impl Qemu {
             reset,
             uarts,
             vbus_sense,
+            _usb_host: usb_host,
             log,
             spi,
             i2cs,