[PATCH 2/7] gpu: nova-core: gsp: add mechanism to wait for space on command queue

[Eliot Courtney <ecourtney@nvidia.com>]

Add `allocate_command_with_timeout` which waits for space on the GSP
command queue. It uses a similar timeout to nouveau.

Let `send_command` wait for space to free up in the command queue by
calling `allocate_command_with_timeout`. This is required to
support continuation records which can fill up the queue.

Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
---
 drivers/gpu/nova-core/gsp/cmdq.rs | 42 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs
index 46819a82a51a..baae06de0e09 100644
--- a/drivers/gpu/nova-core/gsp/cmdq.rs
+++ b/drivers/gpu/nova-core/gsp/cmdq.rs
@@ -243,6 +243,16 @@ fn new(dev: &device::Device<device::Bound>) -> Result<Self> {
         }
     }
 
+    fn driver_bytes_available_to_write(&self) -> usize {
+        let tx = self.cpu_write_ptr();
+        let rx = self.gsp_read_ptr();
+        // `rx` and `tx` are both in `0..MSGQ_NUM_PAGES` per the invariants of `gsp_read_ptr` and
+        // `cpu_write_ptr`. The minimum value case is where `rx == 0` and `tx == MSGQ_NUM_PAGES -
+        // 1`, which gives `0 + MSGQ_NUM_PAGES - (MSGQ_NUM_PAGES - 1) - 1 == 0`.
+        let slots = (rx + MSGQ_NUM_PAGES - tx - 1) % MSGQ_NUM_PAGES;
+        num::u32_as_usize(slots) * GSP_PAGE_SIZE
+    }
+
     /// Returns the region of the GSP message queue that the driver is currently allowed to read
     /// from.
     ///
@@ -311,6 +321,25 @@ fn allocate_command(&mut self, size: usize) -> Result<GspCommand<'_>> {
         })
     }
 
+    /// Allocates a region on the command queue that is large enough to send a command of `size`
+    /// bytes, waiting for space to become available.
+    ///
+    /// This returns a [`GspCommand`] ready to be written to by the caller.
+    ///
+    /// # Errors
+    ///
+    /// - `ETIMEDOUT` if space does not become available within the timeout.
+    /// - `EIO` if the command header is not properly aligned.
+    fn allocate_command_with_timeout(&mut self, size: usize) -> Result<GspCommand<'_>> {
+        read_poll_timeout(
+            || Ok(self.driver_bytes_available_to_write()),
+            |available_bytes| *available_bytes >= size_of::<GspMsgElement>() + size,
+            Delta::ZERO,
+            Delta::from_secs(1),
+        )?;
+        self.allocate_command(size)
+    }
+
     // Returns the index of the memory page the GSP will write the next message to.
     //
     // # Invariants
@@ -480,11 +509,18 @@ fn notify_gsp(bar: &Bar0) {
             .write(bar);
     }
 
+    fn command_size<M>(command: &M) -> usize
+    where
+        M: CommandToGsp,
+    {
+        size_of::<M::Command>() + command.variable_payload_len()
+    }
+
     /// Sends `command` to the GSP.
     ///
     /// # Errors
     ///
-    /// - `EAGAIN` if there was not enough space in the command queue to send the command.
+    /// - `ETIMEDOUT` if space does not become available within the timeout.
     /// - `EIO` if the variable payload requested by the command has not been entirely
     ///   written to by its [`CommandToGsp::init_variable_payload`] method.
     ///
@@ -495,8 +531,8 @@ pub(crate) fn send_command<M>(&mut self, bar: &Bar0, command: M) -> Result
         // This allows all error types, including `Infallible`, to be used for `M::InitError`.
         Error: From<M::InitError>,
     {
-        let command_size = size_of::<M::Command>() + command.variable_payload_len();
-        let dst = self.gsp_mem.allocate_command(command_size)?;
+        let command_size = Self::command_size(&command);
+        let dst = self.gsp_mem.allocate_command_with_timeout(command_size)?;
 
         // Extract area for the command itself.
         let (cmd, payload_1) = M::Command::from_bytes_mut_prefix(dst.contents.0).ok_or(EIO)?;

-- 
2.53.0