Merge pull request #3844 from showier-drastic/main

SpiDevice cancel safety: always set CS pin to high on drop

2 files changed, 20 insertions, 0 deletions

diff --git a/embassy-embedded-hal/Cargo.toml b/embassy-embedded-hal/Cargo.toml
index 9dd2e419f..f385963f1 100644
--- a/embassy-embedded-hal/Cargo.toml
+++ b/embassy-embedded-hal/Cargo.toml
@@ -22,6 +22,7 @@ time = ["dep:embassy-time"]
 default = ["time"]
 
 [dependencies]
+embassy-hal-internal = { version = "0.2.0", path = "../embassy-hal-internal" }
 embassy-futures = { version = "0.1.0", path = "../embassy-futures" }
 embassy-sync = { version = "0.6.2", path = "../embassy-sync" }
 embassy-time = { version = "0.4.0", path = "../embassy-time", optional = true }
diff --git a/embassy-embedded-hal/src/shared_bus/asynch/spi.rs b/embassy-embedded-hal/src/shared_bus/asynch/spi.rs
index 30d4ecc36..78709b7d3 100644
--- a/embassy-embedded-hal/src/shared_bus/asynch/spi.rs
+++ b/embassy-embedded-hal/src/shared_bus/asynch/spi.rs
@@ -25,6 +25,7 @@
 //! let display2 = ST7735::new(spi_dev2, dc2, rst2, Default::default(), 160, 128);
 //! ```
 
+use embassy_hal_internal::drop::OnDrop;
 use embassy_sync::blocking_mutex::raw::RawMutex;
 use embassy_sync::mutex::Mutex;
 use embedded_hal_1::digital::OutputPin;
@@ -70,6 +71,14 @@ where
         let mut bus = self.bus.lock().await;
         self.cs.set_low().map_err(SpiDeviceError::Cs)?;
 
+        let cs_drop = OnDrop::new(|| {
+            // This drop guard deasserts CS pin if the async operation is cancelled.
+            // Errors are ignored in this drop handler, as there's nothing we can do about them.
+            // If the async operation is completed without cancellation, this handler will not
+            // be run, and the CS pin will be deasserted with proper error handling.
+            let _ = self.cs.set_high();
+        });
+
         let op_res = 'ops: {
             for op in operations {
                 let res = match op {
@@ -97,6 +106,10 @@ where
 
         // On failure, it's important to still flush and deassert CS.
         let flush_res = bus.flush().await;
+
+        // Now that all the async operations are done, we defuse the CS guard,
+        // and manually set the CS pin low (to better handle the possible errors).
+        cs_drop.defuse();
         let cs_res = self.cs.set_high();
 
         let op_res = op_res.map_err(SpiDeviceError::Spi)?;
@@ -155,6 +168,11 @@ where
         bus.set_config(&self.config).map_err(|_| SpiDeviceError::Config)?;
         self.cs.set_low().map_err(SpiDeviceError::Cs)?;
 
+        let cs_drop = OnDrop::new(|| {
+            // Please see comment in SpiDevice for an explanation of this drop handler.
+            let _ = self.cs.set_high();
+        });
+
         let op_res = 'ops: {
             for op in operations {
                 let res = match op {
@@ -182,6 +200,7 @@ where
 
         // On failure, it's important to still flush and deassert CS.
         let flush_res = bus.flush().await;
+        cs_drop.defuse();
         let cs_res = self.cs.set_high();
 
         let op_res = op_res.map_err(SpiDeviceError::Spi)?;