[PATCH v3 16/31] gpu: nova-core: gsp: factor out NVKV payload conversion

[Zhi Wang <zhiw@nvidia.com>]

Both GSP initialization and vGPU property queries decode their replies as
NVKV streams.

Move the byte-to-word conversion helper into the NVKV module and make
that module accessible to the vGPU firmware interface.

No functional change is intended.

Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 drivers/gpu/nova-core/gsp.rs          |  2 +-
 drivers/gpu/nova-core/gsp/commands.rs | 17 ++--------------
 drivers/gpu/nova-core/gsp/nvkv.rs     | 28 +++++++++++++++++++++++++++
 3 files changed, 31 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp.rs b/drivers/gpu/nova-core/gsp.rs
index 3dbc37a3b35b..25b4bf6eb848 100644
--- a/drivers/gpu/nova-core/gsp.rs
+++ b/drivers/gpu/nova-core/gsp.rs
@@ -28,7 +28,7 @@
 pub(crate) mod cmdq;
 pub(crate) mod commands;
 mod fw;
-mod nvkv;
+pub(crate) mod nvkv;
 mod regs;
 
 pub(crate) use fw::{
diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
index 97e32f81a39b..742e46efd413 100644
--- a/drivers/gpu/nova-core/gsp/commands.rs
+++ b/drivers/gpu/nova-core/gsp/commands.rs
@@ -22,6 +22,7 @@
             GMCAPI_CMD_GSP_SUSPEND, //
         },
         nvkv::{
+            nvkv_words,
             Decoder,
             Encodable,
             EncodedStream,
@@ -30,7 +31,6 @@
         },
         GspBootContext, //
     },
-    sbuffer::SBufferIter,
     vgpu::VgpuState, //
 };
 
@@ -132,20 +132,7 @@ pub(crate) fn gsp_init(
 ///   or omits a required key, or the FIFO engine count exceeds the supported table capacity.
 /// - `ENOMEM` if the words or the decoded regions cannot be allocated.
 fn decode_gsp_init_reply(payload_0: &[u8], payload_1: &[u8]) -> Result<GspStaticInfo> {
-    const WORD_SIZE: usize = size_of::<u64>();
-
-    let len = payload_0.len() + payload_1.len();
-    if len % WORD_SIZE != 0 {
-        return Err(EINVAL);
-    }
-
-    let mut words = KVVec::with_capacity(len / WORD_SIZE, GFP_KERNEL)?;
-    let mut bytes = SBufferIter::new_reader([payload_0, payload_1]);
-    for _ in 0..len / WORD_SIZE {
-        let mut word = [0u8; WORD_SIZE];
-        bytes.read_exact(&mut word)?;
-        words.push(u64::from_le_bytes(word), GFP_KERNEL)?;
-    }
+    let words = nvkv_words(payload_0, payload_1)?;
 
     let decoder = Decoder::new(&words, UnknownKeyPolicy::Ignore);
     let mut schema = GspInitResponseSchema::default();
diff --git a/drivers/gpu/nova-core/gsp/nvkv.rs b/drivers/gpu/nova-core/gsp/nvkv.rs
index e7a9549919fb..05b1ba5a4f39 100644
--- a/drivers/gpu/nova-core/gsp/nvkv.rs
+++ b/drivers/gpu/nova-core/gsp/nvkv.rs
@@ -27,6 +27,34 @@
 };
 use zerocopy::Immutable;
 
+use crate::sbuffer::SBufferIter;
+
+/// Joins the two halves of a wrapped payload into the `u64` words an NVKV stream is made of.
+///
+/// # Errors
+///
+/// - `EINVAL` if the combined length is not a whole number of words.
+/// - `ENOMEM` if the buffer cannot be allocated.
+pub(crate) fn nvkv_words(payload_0: &[u8], payload_1: &[u8]) -> Result<KVVec<u64>> {
+    const WORD_SIZE: usize = size_of::<u64>();
+
+    // Each byte slice is at most `isize::MAX` bytes, so their sum fits in `usize`.
+    let len = payload_0.len() + payload_1.len();
+    if len % WORD_SIZE != 0 {
+        return Err(EINVAL);
+    }
+
+    let mut words = KVVec::with_capacity(len / WORD_SIZE, GFP_KERNEL)?;
+    let mut bytes = SBufferIter::new_reader([payload_0, payload_1]);
+    for _ in 0..len / WORD_SIZE {
+        let mut word = [0u8; WORD_SIZE];
+        bytes.read_exact(&mut word)?;
+        words.push(u64::from_le_bytes(word), GFP_KERNEL)?;
+    }
+
+    Ok(words)
+}
+
 mod encode;
 pub(crate) use encode::*;