[PATCH] gpu: nova-core: vbios: change PmuLookupTableEntry to relax alignment

[PATCH] gpu: nova-core: vbios: change PmuLookupTableEntry to relax alignment

[Rhys Lloyd]

Instead of the data field containing a u32 and changing the alignment,
change data to [u8; 4] and convert to u32 with a helper function.
Removes another magic number by making the struct the same size as
the data it needs to read, allowing the use of
`size_of::<PmuLookupTableEntry>()`

Signed-off-by: Rhys Lloyd <krakow20@gmail.com>
---
 drivers/gpu/nova-core/vbios.rs | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
index 5b5d9f38cbb3..40244485283c 100644
--- a/drivers/gpu/nova-core/vbios.rs
+++ b/drivers/gpu/nova-core/vbios.rs
@@ -896,21 +896,26 @@ fn try_from(base: BiosImageBase) -> Result<Self> {
 struct PmuLookupTableEntry {
     application_id: u8,
     target_id: u8,
-    data: u32,
+    data: [u8; 4],
 }
 
 impl PmuLookupTableEntry {
     fn new(data: &[u8]) -> Result<Self> {
-        if data.len() < 6 {
+        if data.len() < core::mem::size_of::<Self>() {
             return Err(EINVAL);
         }
 
         Ok(PmuLookupTableEntry {
             application_id: data[0],
             target_id: data[1],
-            data: u32::from_le_bytes(data[2..6].try_into().map_err(|_| EINVAL)?),
+            data: [data[2], data[3], data[4], data[5]],
         })
     }
+
+    /// Construct a u32 from `self.data`.
+    fn get_data(&self) -> u32 {
+        u32::from_le_bytes(self.data)
+    }
 }
 
 /// The [`PmuLookupTableEntry`] structure is used to find the [`PmuLookupTableEntry`] for a given
@@ -1037,7 +1042,7 @@ fn setup_falcon_data(
             .find_entry_by_type(FALCON_UCODE_ENTRY_APPID_FWSEC_PROD)
         {
             Ok(entry) => {
-                let mut ucode_offset = entry.data as usize;
+                let mut ucode_offset = entry.get_data() as usize;
                 ucode_offset -= pci_at_image.base.data.len();
                 if ucode_offset < first_fwsec.base.data.len() {
                     dev_err!(pdev.as_ref(), "Falcon Ucode offset not in second Fwsec.\n");

base-commit: 215a3f91713383a3c0d2da82d223a608a3c17ac1
prerequisite-patch-id: d80f92d314a0693d4c89ffb7810d9ab6990336fa
-- 
2.50.1

[PATCH] gpu: nova-core: vbios: split out PmuLookupTableHeader from PmuLookupTable

[Rhys Lloyd]

Separating the header allows the use of `size_of::<PmuLookupTableHeader>()`
instead of the magic number 4.

Signed-off-by: Rhys Lloyd <krakow20@gmail.com>
---
 drivers/gpu/nova-core/vbios.rs | 56 +++++++++++++++++++++-------------
 1 file changed, 35 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
index 663fc50e8b66..20011c5c9bbc 100644
--- a/drivers/gpu/nova-core/vbios.rs
+++ b/drivers/gpu/nova-core/vbios.rs
@@ -889,6 +889,32 @@ fn try_from(base: BiosImageBase) -> Result<Self> {
     }
 }
 
+/// The [`PmuLookupTableHeader`] structure is header information for [`PmuLookupTable`].
+///
+/// See the [`PmuLookupTable`] description for more information.
+#[expect(dead_code)]
+struct PmuLookupTableHeader {
+    version: u8,
+    header_len: u8,
+    entry_len: u8,
+    entry_count: u8,
+}
+
+impl PmuLookupTableHeader {
+    fn new(data: &[u8]) -> Result<Self> {
+        if data.len() < core::mem::size_of::<Self>() {
+            return Err(EINVAL);
+        }
+
+        Ok(PmuLookupTableHeader {
+            version: data[0],
+            header_len: data[1],
+            entry_len: data[2],
+            entry_count: data[3],
+        })
+    }
+}
+
 /// The [`PmuLookupTableEntry`] structure is a single entry in the [`PmuLookupTable`].
 ///
 /// See the [`PmuLookupTable`] description for more information.
@@ -918,24 +944,18 @@ fn new(data: &[u8]) -> Result<Self> {
 ///
 /// The table of entries is pointed to by the falcon data pointer in the BIT table, and is used to
 /// locate the Falcon Ucode.
-#[expect(dead_code)]
 struct PmuLookupTable {
-    version: u8,
-    header_len: u8,
-    entry_len: u8,
-    entry_count: u8,
+    header: PmuLookupTableHeader,
     table_data: KVec<u8>,
 }
 
 impl PmuLookupTable {
     fn new(pdev: &pci::Device, data: &[u8]) -> Result<Self> {
-        if data.len() < 4 {
-            return Err(EINVAL);
-        }
+        let header = PmuLookupTableHeader::new(data)?;
 
-        let header_len = data[1] as usize;
-        let entry_len = data[2] as usize;
-        let entry_count = data[3] as usize;
+        let header_len = header.header_len as usize;
+        let entry_len = header.entry_len as usize;
+        let entry_count = header.entry_count as usize;
 
         let required_bytes = header_len + (entry_count * entry_len);
 
@@ -963,27 +983,21 @@ fn new(pdev: &pci::Device, data: &[u8]) -> Result<Self> {
             );
         }
 
-        Ok(PmuLookupTable {
-            version: data[0],
-            header_len: header_len as u8,
-            entry_len: entry_len as u8,
-            entry_count: entry_count as u8,
-            table_data,
-        })
+        Ok(PmuLookupTable { header, table_data })
     }
 
     fn lookup_index(&self, idx: u8) -> Result<PmuLookupTableEntry> {
-        if idx >= self.entry_count {
+        if idx >= self.header.entry_count {
             return Err(EINVAL);
         }
 
-        let index = (idx as usize) * self.entry_len as usize;
+        let index = (idx as usize) * self.header.entry_len as usize;
         PmuLookupTableEntry::new(&self.table_data[index..])
     }
 
     // find entry by type value
     fn find_entry_by_type(&self, entry_type: u8) -> Result<PmuLookupTableEntry> {
-        for i in 0..self.entry_count {
+        for i in 0..self.header.entry_count {
             let entry = self.lookup_index(i)?;
             if entry.application_id == entry_type {
                 return Ok(entry);

base-commit: 215a3f91713383a3c0d2da82d223a608a3c17ac1
-- 
2.50.1

Re: [PATCH] gpu: nova-core: vbios: split out PmuLookupTableHeader from PmuLookupTable

[Alexandre Courbot]

On Mon Jul 14, 2025 at 7:43 PM JST, Rhys Lloyd wrote:
> Separating the header allows the use of `size_of::<PmuLookupTableHeader>()`
> instead of the magic number 4.
>
> Signed-off-by: Rhys Lloyd <krakow20@gmail.com>
> ---
>  drivers/gpu/nova-core/vbios.rs | 56 +++++++++++++++++++++-------------
>  1 file changed, 35 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
> index 663fc50e8b66..20011c5c9bbc 100644
> --- a/drivers/gpu/nova-core/vbios.rs
> +++ b/drivers/gpu/nova-core/vbios.rs
> @@ -889,6 +889,32 @@ fn try_from(base: BiosImageBase) -> Result<Self> {
>      }
>  }
>  
> +/// The [`PmuLookupTableHeader`] structure is header information for [`PmuLookupTable`].
> +///
> +/// See the [`PmuLookupTable`] description for more information.
> +#[expect(dead_code)]
> +struct PmuLookupTableHeader {
> +    version: u8,
> +    header_len: u8,
> +    entry_len: u8,
> +    entry_count: u8,
> +}
> +
> +impl PmuLookupTableHeader {

Can you add a 

  // TODO[TRSM]: use FromBytes::from_bytes when it becomes available.

as ultimately that's what we want to do.

(we are using these markers to keep track of tasks to complete as Rust
features land, see Documentation/gpu/nova/core/todo.rst)

> +    fn new(data: &[u8]) -> Result<Self> {
> +        if data.len() < core::mem::size_of::<Self>() {
> +            return Err(EINVAL);
> +        }
> +
> +        Ok(PmuLookupTableHeader {
> +            version: data[0],

How about making `PmuLookupTableHeader` `#[repr(C)]` and using
`offset_of!`? This will also set the stage for the transition to using
`FromBytes::from_bytes`.

[PATCH] gpu: nova-core: vbios: use size_of instead of magic number

[Rhys Lloyd]

12 is identical to the value of `size_of::<BitHeader>()`,
so use the latter instead.

Signed-off-by: Rhys Lloyd <krakow20@gmail.com>
---
 drivers/gpu/nova-core/vbios.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
index 663fc50e8b66..ac35415b4ffb 100644
--- a/drivers/gpu/nova-core/vbios.rs
+++ b/drivers/gpu/nova-core/vbios.rs
@@ -365,7 +365,7 @@ struct BitHeader {
 
 impl BitHeader {
     fn new(data: &[u8]) -> Result<Self> {
-        if data.len() < 12 {
+        if data.len() < core::mem::size_of::<Self>() {
             return Err(EINVAL);
         }
 

base-commit: 215a3f91713383a3c0d2da82d223a608a3c17ac1
-- 
2.50.1

Re: [PATCH] gpu: nova-core: vbios: use size_of instead of magic number

[Alexandre Courbot]

On Mon Jul 14, 2025 at 7:43 PM JST, Rhys Lloyd wrote:
> 12 is identical to the value of `size_of::<BitHeader>()`,
> so use the latter instead.
>
> Signed-off-by: Rhys Lloyd <krakow20@gmail.com>
> ---
>  drivers/gpu/nova-core/vbios.rs | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
> index 663fc50e8b66..ac35415b4ffb 100644
> --- a/drivers/gpu/nova-core/vbios.rs
> +++ b/drivers/gpu/nova-core/vbios.rs
> @@ -365,7 +365,7 @@ struct BitHeader {
>  
>  impl BitHeader {
>      fn new(data: &[u8]) -> Result<Self> {
> -        if data.len() < 12 {
> +        if data.len() < core::mem::size_of::<Self>() {

I agree, but would feel better if we also made `BitHeader` `#[repr(C)]`
to really guarantee this.

(or please educate me if this is unneeded :))

Re: [PATCH] gpu: nova-core: vbios: change PmuLookupTableEntry to relax alignment

[Benno Lossin]

On Mon Jul 14, 2025 at 12:43 PM CEST, Rhys Lloyd wrote:
> +
> +    /// Construct a u32 from `self.data`.
> +    fn get_data(&self) -> u32 {

Getters in Rust usually don't start with `get_`. Using `data(&self)`
here also looks better IMO.

---
Cheers,
Benno

> +        u32::from_le_bytes(self.data)
> +    }
>  }