[PATCH v4 05/10] gpu: nova-core: gsp: cmdq: split RPC parsing part of the receive path

[Alexandre Courbot <acourbot@nvidia.com>]

The RPC parsing should not be done in the same method as the transport
header parsing. Split it out and introduce a `RpcMessage` type to
indicate messages that have been successfully parsed as RPC. This makes
the code easier to move around into its new destination.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
 drivers/gpu/nova-core/gsp/cmdq.rs | 112 ++++++++++++++++++++++++--------------
 1 file changed, 70 insertions(+), 42 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs
index dee2520d3124..2ffb8f4b2ef4 100644
--- a/drivers/gpu/nova-core/gsp/cmdq.rs
+++ b/drivers/gpu/nova-core/gsp/cmdq.rs
@@ -554,11 +554,69 @@ struct GspCommand<'a> {
 struct GspMessage<'a> {
     // Reference to the header of the message.
     header: &'a GspMsgElement,
-    // Slices to the contents of the message. The second slice is zero unless the message loops
+    // Slices to the contents of the message. The second slice is empty unless the message loops
     // over the message queue.
     contents: (&'a [u8], &'a [u8]),
 }
 
+/// A RPC message ready to be processed from the message queue.
+struct RpcMessage<'a> {
+    // Reference to the RPC header of the message.
+    header: &'a RpcMessageHeader,
+    // Slices to the contents of the message. The second slice is empty unless the message loops
+    // over the message queue.
+    contents: (&'a [u8], &'a [u8]),
+}
+
+impl<'a> RpcMessage<'a> {
+    /// Validate the RPC layer of `element` and returns its RPC header and its contents trimmed down
+    /// to the RPC payload.
+    ///
+    /// # Errors
+    ///
+    /// - `EIO` if the element is shorter than the payload length advertised by the RPC header.
+    fn parse(dev: &device::Device, element: GspMessage<'a>) -> Result<RpcMessage<'a>> {
+        let GspMessage {
+            header,
+            contents: (slice_1, slice_2),
+        } = element;
+
+        let rpc_header = header.rpc_header();
+        let payload_length = rpc_header.rpc_length();
+
+        dev_dbg!(
+            dev,
+            "GSP RPC: receive: seq# {}, function={:?}, length=0x{:x}\n",
+            rpc_header.sequence(),
+            rpc_header.function(),
+            payload_length,
+        );
+
+        // Check that the driver read area is large enough for the message.
+        if slice_1.len() + slice_2.len() < payload_length {
+            return Err(EIO);
+        }
+
+        // Cut the message slices down to the actual length of the message.
+        let (slice_1, slice_2) = if slice_1.len() > payload_length {
+            // PANIC: we checked above that `slice_1` is at least as long as `payload_length`.
+            (slice_1.split_at(payload_length).0, &slice_2[0..0])
+        } else {
+            (
+                slice_1,
+                // PANIC: we checked above that `slice_1.len() + slice_2.len()` is at least as
+                // large as `payload_length`.
+                slice_2.split_at(payload_length - slice_1.len()).0,
+            )
+        };
+
+        Ok(RpcMessage {
+            header: rpc_header,
+            contents: (slice_1, slice_2),
+        })
+    }
+}
+
 /// GSP command queue.
 ///
 /// Provides the ability to send commands and receive messages from the GSP using a shared memory
@@ -841,35 +899,6 @@ fn wait_for_msg(&self, timeout: Delta) -> Result<GspMessage<'_>> {
             return Err(EIO);
         }
 
-        let rpc_header = header.rpc_header();
-        let payload_length = rpc_header.rpc_length();
-
-        dev_dbg!(
-            &self.dev,
-            "GSP RPC: receive: seq# {}, function={:?}, length=0x{:x}\n",
-            rpc_header.sequence(),
-            rpc_header.function(),
-            payload_length,
-        );
-
-        // Check that the driver read area is large enough for the message.
-        if slice_1.len() + slice_2.len() < payload_length {
-            return Err(EIO);
-        }
-
-        // Cut the message slices down to the actual length of the message.
-        let (slice_1, slice_2) = if slice_1.len() > payload_length {
-            // PANIC: we checked above that `slice_1` is at least as long as `payload_length`.
-            (slice_1.split_at(payload_length).0, &slice_2[0..0])
-        } else {
-            (
-                slice_1,
-                // PANIC: we checked above that `slice_1.len() + slice_2.len()` is at least as
-                // large as `payload_length`.
-                slice_2.split_at(payload_length - slice_1.len()).0,
-            )
-        };
-
         Ok(GspMessage {
             header,
             contents: (slice_1, slice_2),
@@ -897,14 +926,15 @@ fn receive_msg<M: MessageFromGsp>(&mut self, timeout: Delta) -> Result<M>
         Error: From<M::InitError>,
     {
         let message = self.wait_for_msg(timeout)?;
-        let rpc_header = message.header.rpc_header();
-        let function = rpc_header.function();
-        let seq = rpc_header.sequence();
+        let elem_count = u32::try_from(message.header.msg_length().div_ceil(GSP_PAGE_SIZE))?;
+        let rpc_message = RpcMessage::parse(self.dev, message)?;
+        let function = rpc_message.header.function();
 
         // An early return here would leave the read pointer on this message.
         let result = if matches!(function, Ok(f) if f == M::FUNCTION) {
-            let (cmd, contents_1) = M::Message::from_bytes_prefix(message.contents.0).ok_or(EIO)?;
-            let mut sbuffer = SBufferIter::new_reader([contents_1, message.contents.1]);
+            let (cmd, contents_1) =
+                M::Message::from_bytes_prefix(rpc_message.contents.0).ok_or(EIO)?;
+            let mut sbuffer = SBufferIter::new_reader([contents_1, rpc_message.contents.1]);
 
             M::read(cmd, &mut sbuffer)
                 .map_err(|e| e.into())
@@ -918,15 +948,13 @@ fn receive_msg<M: MessageFromGsp>(&mut self, timeout: Delta) -> Result<M>
                     }
                 })
         } else {
-            self.log_event(function, seq);
+            self.log_event(function, rpc_message.header.sequence());
 
             Err(ENOMSG)
         };
 
         // Advance the read pointer past this message.
-        self.gsp_mem.advance_cpu_read_ptr(u32::try_from(
-            message.header.msg_length().div_ceil(GSP_PAGE_SIZE),
-        )?);
+        self.gsp_mem.advance_cpu_read_ptr(elem_count);
 
         result
     }
@@ -1008,9 +1036,9 @@ fn drain(&mut self) -> Result {
                     dev_err!(&self.dev, "GSP drain: message length overflow\n");
                     EIO
                 })?;
-            let rpc_header = msg.header.rpc_header();
-            let function = rpc_header.function();
-            let seq = rpc_header.sequence();
+            let rpc_msg = RpcMessage::parse(self.dev, msg)?;
+            let function = rpc_msg.header.function();
+            let seq = rpc_msg.header.sequence();
 
             self.gsp_mem.advance_cpu_read_ptr(pages);
             self.log_event(function, seq);

-- 
2.56.0