[PATCH v4 17/32] gpu: nova-core: gsp: factor out NVKV payload conversion

[Alok Kumar <alkumar@nvidia.com>]

From: 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>
Signed-off-by: Alok Kumar <alkumar@nvidia.com>
---
 drivers/gpu/nova-core/gsp.rs              |  2 +-
 drivers/gpu/nova-core/gsp/commands/gmc.rs | 12 ++-------
 drivers/gpu/nova-core/gsp/nvkv.rs         | 31 ++++++++++++++++++++++-
 3 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp.rs b/drivers/gpu/nova-core/gsp.rs
index cac123cbeac4..8424aa3937e7 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/gmc.rs b/drivers/gpu/nova-core/gsp/commands/gmc.rs
index 6f88c99349ac..33aea614cf72 100644
--- a/drivers/gpu/nova-core/gsp/commands/gmc.rs
+++ b/drivers/gpu/nova-core/gsp/commands/gmc.rs
@@ -29,6 +29,7 @@
             GmcCommandId, //
         },
         nvkv::{
+            nvkv_words,
             Decoder,
             Encodable,
             Encoder,
@@ -151,16 +152,7 @@ impl MessageFromGsp for GspStaticInfo {
     fn read(payload: &mut SBufferIter<core::array::IntoIter<&[u8], 2>>) -> Result<Self> {
         let bytes = payload.flush_into_kvec(GFP_KERNEL)?;
 
-        let chunks = bytes.chunks_exact(size_of::<u64>());
-        if !chunks.remainder().is_empty() {
-            return Err(EINVAL);
-        }
-        let mut words = KVVec::with_capacity(chunks.len(), GFP_KERNEL)?;
-        for chunk in chunks {
-            // `chunks_exact` yields slices of exactly `size_of::<u64>()` bytes.
-            let word = chunk.try_into().map_err(|_| EINVAL)?;
-            words.push(u64::from_le_bytes(word), GFP_KERNEL)?;
-        }
+        let words = nvkv_words(&bytes, &[])?;
 
         let decoder = Decoder::new(&words, UnknownKeyPolicy::Ignore);
         let mut schema = KBox::init(GspInitResponseSchema::init(), GFP_KERNEL)?;
diff --git a/drivers/gpu/nova-core/gsp/nvkv.rs b/drivers/gpu/nova-core/gsp/nvkv.rs
index f81a9e60d89c..5887a61af02a 100644
--- a/drivers/gpu/nova-core/gsp/nvkv.rs
+++ b/drivers/gpu/nova-core/gsp/nvkv.rs
@@ -20,11 +20,40 @@
 use kernel::{
     alloc::ArrayVec,
     bitfield,
-    num::Bounded, //
+    num::Bounded,
+    prelude::*, //
 };
 
 use crate::bounded_enum;
 
+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::*;
 
-- 
2.53.0