[PATCH 23/27] gpu: nova-core: gsp: send GSP_INIT and decode its reply

[John Hubbard <jhubbard@nvidia.com>]

GSP-RM answers a GSP_INIT request with the static GPU configuration, and
that reply is also what signals it has finished starting. It raises
load-and-execute events in the meantime, so a caller must handle them
rather than wait through them.

Nova-core can build the request but cannot send it: the GMC sender is
private, and the receive path drops the field carrying the reply status.

Add the sender and the receive-side status field it needs, and decode
the reply into the static-info type the RPC path already produces.

Assisted-by: Cursor:claude-opus-5
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/gpu/nova-core/gsp/cmdq.rs        |  49 ++++++--
 drivers/gpu/nova-core/gsp/commands.rs    | 140 ++++++++++++++++++++++-
 drivers/gpu/nova-core/gsp/fw.rs          |   4 +
 drivers/gpu/nova-core/gsp/fw/commands.rs |  35 +++++-
 4 files changed, 213 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs
index 7da61bc9ad92..82ff46620911 100644
--- a/drivers/gpu/nova-core/gsp/cmdq.rs
+++ b/drivers/gpu/nova-core/gsp/cmdq.rs
@@ -790,22 +790,43 @@ fn receive_msg<M: MessageFromGsp>(&self, timeout: Delta) -> Result<M>
         self.inner.lock().receive_msg(timeout, None)
     }
 
-    /// Receives one GMC event from the GSP and passes its command id and raw payload slices to
-    /// `handler`.
+    /// Receives one GMC element from the GSP and passes its command id, the `max_resp_or_status`
+    /// field, and the raw payload slices to `handler`.
     ///
     /// This method may sleep while waiting. The [`CmdqInner`] mutex stays locked across the wait
     /// and across the `handler` call, so `handler` must not call back into this [`Cmdq`].
     ///
     /// See [`CmdqInner::receive_gmc_and_dispatch`] for return values, queue state, and errors.
-    #[expect(dead_code)]
     pub(crate) fn receive_gmc_and_dispatch<R>(
         &self,
         timeout: Delta,
-        handler: impl FnOnce(u32, &[u8], &[u8]) -> Option<R>,
+        handler: impl FnOnce(u32, u32, &[u8], &[u8]) -> Option<R>,
     ) -> Result<Option<R>> {
         self.inner.lock().receive_gmc_and_dispatch(timeout, handler)
     }
 
+    /// Sends a GMC API command to the GSP without waiting for its response.
+    ///
+    /// A caller that expects a response reads it with [`Self::receive_gmc_and_dispatch`], which
+    /// lets it handle the events GSP-RM interleaves before the response arrives.
+    ///
+    /// # Errors
+    ///
+    /// - `EMSGSIZE` if the command exceeds the maximum queue element size.
+    /// - `ETIMEDOUT` if space does not become available within the timeout.
+    /// - `EIO` if the command header is not properly aligned.
+    pub(crate) fn send_gmc_no_wait(
+        &self,
+        bar: Bar0<'_>,
+        command_id: u32,
+        payload: &[u8],
+        max_response_size: u32,
+    ) -> Result {
+        self.inner
+            .lock()
+            .send_gmc(bar, command_id, payload, max_response_size)
+    }
+
     /// Waits for an unsolicited GSP event of type `M`, dispatching any other event that arrives
     /// first.
     ///
@@ -1005,7 +1026,6 @@ fn send_command<M>(&mut self, bar: Bar0<'_>, command: M) -> Result<u32>
     /// - `EMSGSIZE` if the command exceeds the maximum queue element size.
     /// - `ETIMEDOUT` if space does not become available within the timeout.
     /// - `EIO` if the command header is not properly aligned.
-    #[expect(dead_code)]
     fn send_gmc(
         &mut self,
         bar: Bar0<'_>,
@@ -1383,9 +1403,13 @@ fn wait_for_gmc_msg(&self, timeout: Delta) -> Result<GmcMessage<'_>> {
 
     /// Receive the next GMC event from the GSP and dispatch it through a handler.
     ///
-    /// The handler receives the GMC command id and the raw payload slices that follow the
-    /// [`super::fw::GmcApiHeader`] (two slices because the circular buffer may wrap). It returns
-    /// `None` for an event it does not handle.
+    /// The handler receives the GMC command id, the header's `max_resp_or_status` field, and the
+    /// raw payload slices that follow the [`super::fw::GmcApiHeader`] (two slices because the
+    /// circular buffer may wrap). It returns `None` for an element it does not handle.
+    ///
+    /// `max_resp_or_status` is a union: GSP-RM writes an `NV_STATUS` there when the element is a
+    /// response, and the maximum response size when it is a request. Only a handler that knows
+    /// which one it asked for can read it.
     ///
     /// Where [`Self::receive_msg`] keys on [`MsgFunction`], this keys on the GMC command id,
     /// which is the form the r000 firmware uses for boot events.
@@ -1401,7 +1425,7 @@ fn wait_for_gmc_msg(&self, timeout: Delta) -> Result<GmcMessage<'_>> {
     fn receive_gmc_and_dispatch<R>(
         &mut self,
         timeout: Delta,
-        handler: impl FnOnce(u32, &[u8], &[u8]) -> Option<R>,
+        handler: impl FnOnce(u32, u32, &[u8], &[u8]) -> Option<R>,
     ) -> Result<Option<R>> {
         let message = self.wait_for_gmc_msg(timeout)?;
         let header = message.header;
@@ -1420,7 +1444,12 @@ fn receive_gmc_and_dispatch<R>(
                 length,
             );
 
-            handler(command_id, message.contents.0, message.contents.1)
+            handler(
+                command_id,
+                header.gmc.max_resp_or_status,
+                message.contents.0,
+                message.contents.1,
+            )
         } else {
             dev_warn!(&self.dev, "GSP GMC: dropping non-GMC queue element\n");
             None
diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
index 0c3832ccf726..d55faf1a4e04 100644
--- a/drivers/gpu/nova-core/gsp/commands.rs
+++ b/drivers/gpu/nova-core/gsp/commands.rs
@@ -20,6 +20,7 @@
 };
 
 use crate::{
+    driver::Bar0,
     gpu::Chipset,
     gsp::{
         cmdq::{
@@ -32,13 +33,18 @@
             self,
             commands::{
                 GspInitRequest,
+                GspInitResponse,
+                GspInitResponseSchema,
                 RegKey, //
             },
-            MsgFunction, //
+            MsgFunction,
+            GMCAPI_CMD_GSP_INIT, //
         },
         nvkv::{
+            Decoder,
             Encodeable,
-            Encoder, //
+            Encoder,
+            UnknownKeyPolicy, //
         },
     },
     sbuffer::SBufferIter,
@@ -311,6 +317,136 @@ pub(crate) fn build_gsp_init_payload(
     Ok(encoder.finish())
 }
 
+/// Size of the buffer GSP-RM may fill with static configuration, matching the allocation Open RM
+/// makes in `kgspSendInitRpcs`.
+const GSP_INIT_MAX_RESPONSE_SIZE: u32 = 48 * 1024;
+
+/// Sends `GSP_INIT` and returns the static configuration its reply carries.
+///
+/// GSP-RM interleaves load-and-execute events between the request and the reply, and those events
+/// drive the falcon loads that let it finish starting, so each one is passed to `on_boot_event`
+/// rather than skipped. The reply arrives only once GSP-RM is up, which is what makes it the
+/// signal that boot is complete.
+///
+/// `payload` is the blob from [`build_gsp_init_payload`].
+///
+/// # Errors
+///
+/// - `EIO` if GSP-RM reports a failure status, or if the reply is not a whole number of NVKV
+///   words.
+/// - `ETIMEDOUT` if neither the reply nor another element arrives within
+///   [`Cmdq::RECEIVE_TIMEOUT`].
+///
+/// Errors from `on_boot_event` and from decoding the reply are propagated as-is.
+#[expect(dead_code)]
+pub(crate) fn gsp_init(
+    cmdq: &Cmdq,
+    bar: Bar0<'_>,
+    payload: &[u64],
+    mut on_boot_event: impl FnMut(u32, &[u8]) -> Result,
+) -> Result<GetGspStaticInfoReply> {
+    // Qualified because `zerocopy::IntoBytes` also gives `[T]` an `as_bytes`.
+    let payload = AsBytes::as_bytes(payload);
+
+    cmdq.send_gmc_no_wait(
+        bar,
+        GMCAPI_CMD_GSP_INIT,
+        payload,
+        GSP_INIT_MAX_RESPONSE_SIZE,
+    )?;
+
+    loop {
+        let reply = cmdq.receive_gmc_and_dispatch(
+            Cmdq::RECEIVE_TIMEOUT,
+            |command_id, max_resp_or_status, payload_0, payload_1| {
+                if command_id == GMCAPI_CMD_GSP_INIT {
+                    Some(decode_gsp_init_reply(
+                        max_resp_or_status,
+                        payload_0,
+                        payload_1,
+                    ))
+                } else {
+                    // A boot event. Keep waiting for the reply unless handling it failed.
+                    match on_boot_event(command_id, payload_0) {
+                        Ok(()) => None,
+                        Err(e) => Some(Err(e)),
+                    }
+                }
+            },
+        )?;
+
+        if let Some(reply) = reply {
+            return reply;
+        }
+    }
+}
+
+/// Decodes the `GSP_INIT` reply, whose `max_resp_or_status` field carries an `NV_STATUS`.
+fn decode_gsp_init_reply(
+    status: u32,
+    payload_0: &[u8],
+    payload_1: &[u8],
+) -> Result<GetGspStaticInfoReply> {
+    if status != 0 {
+        return Err(EIO);
+    }
+
+    decode_gsp_info(&nvkv_words(payload_0, payload_1)?)
+}
+
+/// Joins the two halves of a wrapped payload into the `u64` words an NVKV stream is made of.
+///
+/// # Errors
+///
+/// - `EIO` if the combined length is not a whole number of words.
+/// - `ENOMEM` if the buffer cannot be allocated.
+fn nvkv_words(payload_0: &[u8], payload_1: &[u8]) -> Result<KVVec<u64>> {
+    let bytes = SBufferIter::new_reader([payload_0, payload_1]).flush_into_kvec(GFP_KERNEL)?;
+    let words = bytes.chunks_exact(size_of::<u64>());
+    if !words.remainder().is_empty() {
+        return Err(EIO);
+    }
+
+    let mut out = KVVec::with_capacity(bytes.len() / size_of::<u64>(), GFP_KERNEL)?;
+    for word in words {
+        let word: [u8; size_of::<u64>()] = word.try_into().map_err(|_| EIO)?;
+        out.push(u64::from_le_bytes(word), GFP_KERNEL)?;
+    }
+
+    Ok(out)
+}
+
+/// Decodes the static GPU configuration from an NVKV stream.
+///
+/// # Errors
+///
+/// - `EINVAL` if the stream is malformed or omits a required key.
+/// - `ENOMEM` if the decoded regions cannot be allocated.
+fn decode_gsp_info(words: &[u64]) -> Result<GetGspStaticInfoReply> {
+    let decoder = Decoder::new(words, UnknownKeyPolicy::Ignore);
+    let decoded = KBox::try_init(
+        decoder.decode(GspInitResponseSchema::default())?,
+        GFP_KERNEL,
+    )?;
+
+    let mut gpu_name = [0u8; GspInitResponse::MAX_GPU_NAME_LEN];
+    let name = decoded.gpu_name();
+    gpu_name
+        .get_mut(..name.len())
+        .ok_or(EINVAL)?
+        .copy_from_slice(name);
+
+    let mut usable_fb_regions = KVec::new();
+    for region in decoded.usable_fb_regions() {
+        usable_fb_regions.push(region, GFP_KERNEL)?;
+    }
+
+    Ok(GetGspStaticInfoReply {
+        gpu_name,
+        usable_fb_regions,
+    })
+}
+
 pub(crate) use fw::commands::PowerStateLevel;
 
 /// The `UnloadingGuestDriver` command, used to shut down the GSP.
diff --git a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
index 4772af362117..6958ee3a2e4e 100644
--- a/drivers/gpu/nova-core/gsp/fw.rs
+++ b/drivers/gpu/nova-core/gsp/fw.rs
@@ -979,6 +979,10 @@ pub(crate) struct GmcApiHeader {
 /// `GMCAPI_HEADER_COMMAND_ID_MASK`. The remaining byte carries flags.
 const GMCAPI_COMMAND_ID_MASK: u32 = 0x00ff_ffff;
 
+/// GMC command that hands GSP-RM its system information and registry keys and returns the static
+/// GPU configuration. Its reply is also what signals that GSP-RM has finished starting.
+pub(crate) const GMCAPI_CMD_GSP_INIT: u32 = r000_00::GMCAPI_COMMANDS_GMCAPI_CMD_GSP_INIT;
+
 /// GMC command asking the driver to run the generic falcon bootloader against a descriptor the
 /// GSP supplies.
 pub(crate) const GMCAPI_CMD_EXEC_GENERIC_BOOTLOADER: u32 =
diff --git a/drivers/gpu/nova-core/gsp/fw/commands.rs b/drivers/gpu/nova-core/gsp/fw/commands.rs
index bfd756813c64..00e40a435053 100644
--- a/drivers/gpu/nova-core/gsp/fw/commands.rs
+++ b/drivers/gpu/nova-core/gsp/fw/commands.rs
@@ -402,7 +402,7 @@ pub(crate) fn new(
     /// Schema for the `GSP_INIT` response.
     #[cfg_attr(not(CONFIG_KUNIT), allow(dead_code))]
     #[derive(Default)]
-    struct GspInitResponseSchema => GspInitResponse {
+    pub(crate) struct GspInitResponseSchema => GspInitResponse {
         gpu_name:
             Array<u8, { GspInitResponse::MAX_GPU_NAME_LEN }, { Self::GPU_NAME_STRING_KEY }>,
         fb_regions: Accumulated<FbRegionSchema>,
@@ -420,7 +420,7 @@ impl GspInitResponseSchema {
 
 /// Payload of the `GSP_INIT` response.
 #[cfg_attr(not(CONFIG_KUNIT), allow(dead_code))]
-struct GspInitResponse {
+pub(crate) struct GspInitResponse {
     gpu_name: ArrayVec<u8, { Self::MAX_GPU_NAME_LEN }>,
     fb_regions: KVVec<FbRegion>,
     bar1_pde_base: u64,
@@ -428,7 +428,36 @@ struct GspInitResponse {
 }
 
 impl GspInitResponse {
-    const MAX_GPU_NAME_LEN: usize = 64;
+    pub(crate) const MAX_GPU_NAME_LEN: usize = 64;
+
+    /// A region with no tag is general-purpose memory. A tagged region is reserved for a
+    /// firmware-internal use that the tag identifies.
+    const FB_REGION_TAG_NONE: u32 = 0;
+
+    /// Returns the GPU name, which GSP-RM sends with its NULL terminator.
+    pub(crate) fn gpu_name(&self) -> &[u8] {
+        self.gpu_name.as_slice()
+    }
+
+    /// Iterates over the FB regions the driver may allocate from.
+    ///
+    /// A region qualifies when it is untagged, unprotected, and supports both compression and
+    /// isochronous access, which is the same set the RPC path selects from
+    /// [`GspStaticConfigInfo::usable_fb_regions`].
+    pub(crate) fn usable_fb_regions(&self) -> impl Iterator<Item = Range<u64>> + '_ {
+        self.fb_regions.iter().filter_map(|region| {
+            if region.limit >= region.base
+                && region.tag == Self::FB_REGION_TAG_NONE
+                && !region.flags.protected()
+                && region.flags.support_compressed()
+                && region.flags.support_iso()
+            {
+                region.limit.checked_add(1).map(|end| region.base..end)
+            } else {
+                None
+            }
+        })
+    }
 }
 
 nvkv_decode! {
-- 
2.55.0