[PATCH RFC 3/4] gpu: nova-core: gsp: derive zerocopy traits for the msgq POD types

[SeungJong Ha via B4 Relay <devnull+engineer.jjhama.gmail.com@kernel.org>]

From: SeungJong Ha <engineer.jjhama@gmail.com>

Replace the hand-audited `unsafe impl transmute::{AsBytes, FromBytes}` on
the msgq header newtypes (`MsgqTxHeader`/`MsgqRxHeader`), `PteArray` and
the generated bindings (`msgqTxHeader`/`msgqRxHeader`) with `zerocopy`
derives. These are padding-free PODs, so the derive applies directly.

The bindings derives are hand-added for the demo; canonically they come
from bindgen's `--with-derive-custom-struct`.

Assisted-by: Claude-Code:claude-opus-4-8
Signed-off-by: SeungJong Ha <engineer.jjhama@gmail.com>
---
 drivers/gpu/nova-core/gsp.rs                      | 13 ++-----------
 drivers/gpu/nova-core/gsp/fw.rs                   |  8 ++++----
 drivers/gpu/nova-core/gsp/fw/r570_144.rs          |  2 ++
 drivers/gpu/nova-core/gsp/fw/r570_144/bindings.rs |  4 ++--
 4 files changed, 10 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/nova-core/gsp.rs b/drivers/gpu/nova-core/gsp.rs
index 69175ca3315c..d7da16e9177a 100644
--- a/drivers/gpu/nova-core/gsp.rs
+++ b/drivers/gpu/nova-core/gsp.rs
@@ -12,11 +12,7 @@
         DmaAddress, //
     },
     pci,
-    prelude::*,
-    transmute::{
-        AsBytes,
-        FromBytes, //
-    }, //
+    prelude::*, //
 };
 
 pub(crate) mod cmdq;
@@ -48,14 +44,9 @@
 
 /// Array of page table entries, as understood by the GSP bootloader.
 #[repr(C)]
+#[derive(FromBytes, IntoBytes, Immutable)]
 struct PteArray<const NUM_ENTRIES: usize>([u64; NUM_ENTRIES]);
 
-/// SAFETY: arrays of `u64` implement `FromBytes` and we are but a wrapper around one.
-unsafe impl<const NUM_ENTRIES: usize> FromBytes for PteArray<NUM_ENTRIES> {}
-
-/// SAFETY: arrays of `u64` implement `AsBytes` and we are but a wrapper around one.
-unsafe impl<const NUM_ENTRIES: usize> AsBytes for PteArray<NUM_ENTRIES> {}
-
 impl<const NUM_PAGES: usize> PteArray<NUM_PAGES> {
     /// Returns the page table entry for `index`, for a mapping starting at `start`.
     // TODO: Replace with `IoView` projection once available.
diff --git a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
index 4db0cfa4dc4d..623ab33847c5 100644
--- a/drivers/gpu/nova-core/gsp/fw.rs
+++ b/drivers/gpu/nova-core/gsp/fw.rs
@@ -696,6 +696,7 @@ fn id8(name: &str) -> u64 {
 
 /// TX header for setting up a message queue with the GSP.
 #[repr(transparent)]
+#[derive(FromBytes, IntoBytes, Immutable)]
 pub(crate) struct MsgqTxHeader(bindings::msgqTxHeader);
 
 impl MsgqTxHeader {
@@ -722,11 +723,11 @@ pub(crate) fn new(msgq_size: u32, rx_hdr_offset: u32, msg_count: u32) -> Self {
     }
 }
 
-// SAFETY: Padding is explicit and does not contain uninitialized data.
-unsafe impl AsBytes for MsgqTxHeader {}
+kernel::impl_transmute_via_zerocopy!(MsgqTxHeader);
 
 /// RX header for setting up a message queue with the GSP.
 #[repr(transparent)]
+#[derive(FromBytes, IntoBytes, Immutable)]
 pub(crate) struct MsgqRxHeader(bindings::msgqRxHeader);
 
 /// Header for the message RX queue.
@@ -737,8 +738,7 @@ pub(crate) fn new() -> Self {
     }
 }
 
-// SAFETY: Padding is explicit and does not contain uninitialized data.
-unsafe impl AsBytes for MsgqRxHeader {}
+kernel::impl_transmute_via_zerocopy!(MsgqRxHeader);
 
 bitfield! {
     struct MsgHeaderVersion(u32) {
diff --git a/drivers/gpu/nova-core/gsp/fw/r570_144.rs b/drivers/gpu/nova-core/gsp/fw/r570_144.rs
index 2e6f0d298756..4b6280fab674 100644
--- a/drivers/gpu/nova-core/gsp/fw/r570_144.rs
+++ b/drivers/gpu/nova-core/gsp/fw/r570_144.rs
@@ -23,6 +23,8 @@
 )]
 use kernel::ffi;
 use pin_init::MaybeZeroable;
+// Hand-added for the demo; canonically emitted by bindgen --with-derive-custom-struct.
+use kernel::prelude::{FromBytes, Immutable, IntoBytes};
 
 include!("r570_144/bindings.rs");
 
diff --git a/drivers/gpu/nova-core/gsp/fw/r570_144/bindings.rs b/drivers/gpu/nova-core/gsp/fw/r570_144/bindings.rs
index ea350f9b2cc4..82b1e8b155f0 100644
--- a/drivers/gpu/nova-core/gsp/fw/r570_144/bindings.rs
+++ b/drivers/gpu/nova-core/gsp/fw/r570_144/bindings.rs
@@ -846,7 +846,7 @@ pub struct PACKED_REGISTRY_TABLE {
     pub entries: __IncompleteArrayField<PACKED_REGISTRY_ENTRY>,
 }
 #[repr(C)]
-#[derive(Debug, Default, Copy, Clone, MaybeZeroable)]
+#[derive(Debug, Default, Copy, Clone, MaybeZeroable, FromBytes, IntoBytes, Immutable)]
 pub struct msgqTxHeader {
     pub version: u32_,
     pub size: u32_,
@@ -858,7 +858,7 @@ pub struct msgqTxHeader {
     pub entryOff: u32_,
 }
 #[repr(C)]
-#[derive(Debug, Default, Copy, Clone, MaybeZeroable)]
+#[derive(Debug, Default, Copy, Clone, MaybeZeroable, FromBytes, IntoBytes, Immutable)]
 pub struct msgqRxHeader {
     pub readPtr: u32_,
 }

-- 
2.54.0