[PATCH 1/5] gpu: nova-core: add Tlv.get_u64

[Timur Tabi <ttabi@nvidia.com>]

Introduce get_u64() to support variable-sized TLV integers.  If the driver
expects that a particular tag might be a 64-bit value, it should use this
method read it.

TLVs can store unsigned integers in either 32-bit or 64-bit little-endian
format.  The script that generates TLV files is written in Python, and
Python integers are arbitrarily sized.  For any given integer, the script
will store it as a 32-bit integer if its value is less than 0x100000000,
without any regard to its purpose.  This means that the driver may not
know until runtime whether a given TLV integer is encoded as four bytes
or eight.

Signed-off-by: Timur Tabi <ttabi@nvidia.com>
---
 drivers/gpu/nova-core/firmware/tlv.rs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/gpu/nova-core/firmware/tlv.rs b/drivers/gpu/nova-core/firmware/tlv.rs
index 7f278903dc8b..75d8f907421b 100644
--- a/drivers/gpu/nova-core/firmware/tlv.rs
+++ b/drivers/gpu/nova-core/firmware/tlv.rs
@@ -257,6 +257,23 @@ pub(crate) fn load_file(
             .ok_or(EINVAL)
     }
 
+    /// Return a u64, from either a 32-bit or 64-bit little-endian tag.
+    #[expect(unused)]
+    pub(crate) fn get_u64(&self, tag: &[u8; 4]) -> Result<u64> {
+        let value = self.get_bytes(tag)?;
+
+        match value.len() {
+            // `value` is an unsized slice, but from_le_bytes() requires a sized
+            // slice (&[u8; N]), so we need to convert.
+            4 => value
+                .first_chunk()
+                .map(|&b| u64::from(u32::from_le_bytes(b))),
+            8 => value.first_chunk().map(|&b| u64::from_le_bytes(b)),
+            _ => None,
+        }
+        .ok_or(EINVAL)
+    }
+
     /// Return a string value.
     pub(crate) fn get_string(&self, tag: &[u8; 4]) -> Result<&'a str> {
         let tlv = self.find(tag)?;
-- 
2.54.0