[opentitanlib,qemu] Add additional SPI console TX sync for QEMU

This is only enabled if the QEMU interface is configured for the SPI
console - any other interface will retain the existing behaviour and
avoid the additional poling from the host side.

For QEMU specifically, we introduce a host-side poll to see the TX ready
pin go low after reading out the header (but before reading out the
payload). This ensures we don't run into synchronization issues due to
emulation for very small SPI transfers in which the entirity of the
header & payload are read out by the host before the device has a chance
to run enough guest SW to signal that the GPIO ready pin should go low.

In such a scenario, the device would look to host SW as if it is ready
to send more data, even though in reality the guest SW has barely
progressed enough to register that the host has started reading, causing
the two devices to get out of sync.

Signed-off-by: Alex Jones <[email protected]>

Author: AlexJones0

sw/host/opentitanlib/src/console/spi.rs

@@ -21,6 +21,7 @@ pub struct SpiConsoleDevice<'a> {
     next_read_address: Cell<u32>,
     device_tx_ready_pin: Option<&'a Rc<dyn GpioPin>>,
     ignore_frame_num: bool,
+    wait_tx_ready_deassert: bool,
 }
 
 impl<'a> SpiConsoleDevice<'a> {
@@ -36,10 +37,16 @@ impl<'a> SpiConsoleDevice<'a> {
         spi: &'a dyn Target,
         device_tx_ready_pin: Option<&'a Rc<dyn GpioPin>>,
         ignore_frame_num: bool,
+        interface: Option<&str>,
     ) -> Result<Self> {
         let flash = SpiFlash {
             ..Default::default()
         };
+        // QEMU is currently the only interface that requires additional
+        // synchronization on the TX-ready indicator pin to avoid timing
+        // & synchronization issues for small transactions, due to its
+        // nature as an emulated interface.
+        let wait_tx_ready_deassert = interface == Some("qemu");
         Ok(Self {
             spi,
             flash,
@@ -48,6 +55,7 @@ impl<'a> SpiConsoleDevice<'a> {
             next_read_address: Cell::new(0),
             device_tx_ready_pin,
             ignore_frame_num,
+            wait_tx_ready_deassert,
         })
     }
 
@@ -75,6 +83,19 @@ impl<'a> SpiConsoleDevice<'a> {
         let mut header = vec![0u8; SpiConsoleDevice::SPI_FRAME_HEADER_SIZE];
         self.read_data(read_address, &mut header)?;
 
+        // When using small (<= 4 byte) SPI transactions on emulation targets,
+        // sometimes the entire transaction can occur before the logic low
+        // transmission of the TX-indicator GPIO is issued, causing the host
+        // to erroneously see the device as ready and start another transaction
+        // whilst the device is still processing the previous. For such targets,
+        // add additional synchronization by waiting for the TX-indicator pin
+        // to go low after reading the header.
+        if let Some(ready_pin) = self.get_tx_ready_pin()? {
+            if self.wait_tx_ready_deassert {
+                while ready_pin.read()? {}
+            }
+        }
+
         let magic_number: u32 = u32::from_le_bytes(header[0..4].try_into().unwrap());
         let frame_number: u32 = u32::from_le_bytes(header[4..8].try_into().unwrap());
         let data_len_bytes: usize = u32::from_le_bytes(header[8..12].try_into().unwrap()) as usize;

sw/host/provisioning/cp/src/main.rs

@@ -54,6 +54,7 @@ fn main() -> Result<()> {
         &*spi,
         Some(device_console_tx_ready_pin),
         /*ignore_frame_num=*/ false,
+        Some(opts.init.backend_opts.interface.as_str()),
     )?;
 
     let provisioning_data = ManufCpProvisioningData {

sw/host/provisioning/ft/src/main.rs

@@ -133,6 +133,7 @@ fn main() -> Result<()> {
         &*spi,
         Some(device_console_tx_ready_pin),
         /*ignore_frame_num=*/ false,
+        Some(opts.init.backend_opts.interface.as_str()),
     )?;
     InitializeTest::print_result("load_bitstream", opts.init.load_bitstream.init(&transport))?;
 

sw/host/tests/chip/ottf_console_with_gpio_tx_indicator/src/main.rs

@@ -46,6 +46,7 @@ fn spi_device_console_test(opts: &Opts, transport: &TransportWrapper) -> Result<
         &*spi,
         Some(device_console_tx_ready_pin),
         /*ignore_frame_num=*/ false,
+        Some(opts.init.backend_opts.interface.as_str()),
     )?;
 
     // Load the ELF binary and get the expect data.

sw/host/tests/chip/spi_device_ottf_console/src/main.rs

@@ -48,7 +48,12 @@ fn spi_device_console_test(opts: &Opts, transport: &TransportWrapper) -> Result<
     let mut stdout = std::io::stdout();
     let spi = transport.spi(&opts.console_spi)?;
 
-    let spi_console_device = SpiConsoleDevice::new(&*spi, None, /*ignore_frame_num=*/ false)?;
+    let spi_console_device = SpiConsoleDevice::new(
+        &*spi,
+        None,
+        /*ignore_frame_num=*/ false,
+        Some(opts.init.backend_opts.interface.as_str()),
+    )?;
     let _ = UartConsole::wait_for(&spi_console_device, r"Running [^\r\n]*", opts.timeout)?;
 
     /* Load the ELF binary and get the expect data.*/

sw/host/tests/chip/spi_device_ujson_console_test/src/main.rs

@@ -109,7 +109,12 @@ fn main() -> Result<()> {
 
     let transport = opts.init.init_target()?;
     let spi = transport.spi(&opts.console_spi)?;
-    let spi_console_device = SpiConsoleDevice::new(&*spi, None, /*ignore_frame_num=*/ false)?;
+    let spi_console_device = SpiConsoleDevice::new(
+        &*spi,
+        None,
+        /*ignore_frame_num=*/ false,
+        Some(opts.init.backend_opts.interface.as_str()),
+    )?;
     let _ = UartConsole::wait_for(&spi_console_device, r"Running [^\r\n]*", opts.timeout)?;
 
     execute_test!(test_perso_blob_strcut, &opts, &spi_console_device);

sw/host/tests/crypto/aes_gcm_nist_kat/src/main.rs

@@ -137,7 +137,12 @@ fn run_aes_gcm_testcase(
 
 fn test_aes_gcm(opts: &Opts, transport: &TransportWrapper) -> Result<()> {
     let spi = transport.spi("BOOTSTRAP")?;
-    let spi_console_device = SpiConsoleDevice::new(&*spi, None, /*ignore_frame_num=*/ false)?;
+    let spi_console_device = SpiConsoleDevice::new(
+        &*spi,
+        None,
+        /*ignore_frame_num=*/ false,
+        Some(opts.init.backend_opts.interface.as_str()),
+    )?;
     let _ = UartConsole::wait_for(&spi_console_device, r"Running [^\r\n]*", opts.timeout)?;
 
     let mut test_counter = 0u32;

sw/host/tests/crypto/aes_nist_kat/src/main.rs

@@ -130,7 +130,12 @@ fn run_aes_testcase(
 
 fn test_aes(opts: &Opts, transport: &TransportWrapper) -> Result<()> {
     let spi = transport.spi("BOOTSTRAP")?;
-    let spi_console_device = SpiConsoleDevice::new(&*spi, None, /*ignore_frame_num=*/ false)?;
+    let spi_console_device = SpiConsoleDevice::new(
+        &*spi,
+        None,
+        /*ignore_frame_num=*/ false,
+        Some(opts.init.backend_opts.interface.as_str()),
+    )?;
     let _ = UartConsole::wait_for(&spi_console_device, r"Running [^\r\n]*", opts.timeout)?;
 
     let mut test_counter = 0u32;

sw/host/tests/crypto/drbg_kat/src/main.rs

@@ -128,7 +128,12 @@ fn run_drbg_testcase(
 
 fn test_drbg(opts: &Opts, transport: &TransportWrapper) -> Result<()> {
     let spi = transport.spi("BOOTSTRAP")?;
-    let spi_console_device = SpiConsoleDevice::new(&*spi, None, /*ignore_frame_num=*/ false)?;
+    let spi_console_device = SpiConsoleDevice::new(
+        &*spi,
+        None,
+        /*ignore_frame_num=*/ false,
+        Some(opts.init.backend_opts.interface.as_str()),
+    )?;
     let _ = UartConsole::wait_for(&spi_console_device, r"Running [^\r\n]*", opts.timeout)?;
 
     let mut test_counter = 0u32;

sw/host/tests/crypto/ecdh_kat/src/main.rs

@@ -220,7 +220,12 @@ fn run_ecdh_testcase(
 
 fn test_ecdh(opts: &Opts, transport: &TransportWrapper) -> Result<()> {
     let spi = transport.spi("BOOTSTRAP")?;
-    let spi_console_device = SpiConsoleDevice::new(&*spi, None, /*ignore_frame_num=*/ false)?;
+    let spi_console_device = SpiConsoleDevice::new(
+        &*spi,
+        None,
+        /*ignore_frame_num=*/ false,
+        Some(opts.init.backend_opts.interface.as_str()),
+    )?;
     let _ = UartConsole::wait_for(&spi_console_device, r"Running [^\r\n]*", opts.timeout)?;
 
     let mut test_counter = 0u32;