linux-kernel - Re: [PATCH v2 1/3] nova-core: Simplify `transmute` and `transmute

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Message-ID: <70210168-ee28-4996-89f0-83f8590cb716@gmail.com>
Date: Sun, 2 Nov 2025 16:09:54 +0100
From: Daniel del Castillo <delcastillodelarosadaniel@...il.com>
To: Alexandre Courbot <acourbot@...dia.com>,
 Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>
Cc: nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org,
 dri-devel <dri-devel-bounces@...ts.freedesktop.org>
Subject: Re: [PATCH v2 1/3] nova-core: Simplify `transmute` and
 `transmute_mut` in fwsec.rs

Hi Alexandre,

On 11/1/25 12:47, Alexandre Courbot wrote:
> On Fri Oct 24, 2025 at 5:51 AM JST, Daniel del Castillo wrote:
>> This patch solves one of the existing mentions of COHA, a task
>> in the Nova task list about improving the `CoherentAllocation` API.
>> It uses the new `from_bytes` method from the `FromBytes` trait as
>> well as the `as_slice` and `as_slice_mut` methods from
>> `CoherentAllocation`.
>>
>> Signed-off-by: Daniel del Castillo <delcastillodelarosadaniel@...il.com>
>>
>> ---
>>
>> I confirmed by talking to Alexandre Courbot, that the reading/writing
>> methods in `CoherentAllocation` can never be safe, so
>> this patch doesn't actually change `CoherentAllocation`, but rather
>> tries to solve one of the existing references to [COHA].
>>
>> V1 -> V2: Split previous patch into two. One per reference to COHA.
>>           Improved comments. Let me know if they are okay now.
>>           Use of `{...}` syntax for the `if let`
>>
>>  drivers/gpu/nova-core/firmware/fwsec.rs | 129 +++++++++++-------------
>>  1 file changed, 60 insertions(+), 69 deletions(-)
>>
>> diff --git a/drivers/gpu/nova-core/firmware/fwsec.rs b/drivers/gpu/nova-core/firmware/fwsec.rs
>> index 8edbb5c0572c..507ef3868565 100644
>> --- a/drivers/gpu/nova-core/firmware/fwsec.rs
>> +++ b/drivers/gpu/nova-core/firmware/fwsec.rs
>> @@ -11,12 +11,12 @@
>>  //! - The ucode signature, so the GSP falcon can run FWSEC in HS mode.
>>  
>>  use core::marker::PhantomData;
>> -use core::mem::{align_of, size_of};
>> +use core::mem::size_of;
>>  use core::ops::Deref;
>>  
>>  use kernel::device::{self, Device};
>>  use kernel::prelude::*;
>> -use kernel::transmute::FromBytes;
>> +use kernel::transmute::{AsBytes, FromBytes};
>>  
>>  use crate::dma::DmaObject;
>>  use crate::driver::Bar0;
>> @@ -35,7 +35,7 @@ struct FalconAppifHdrV1 {
>>      entry_size: u8,
>>      entry_count: u8,
>>  }
>> -// SAFETY: any byte sequence is valid for this struct.
>> +// SAFETY: Any byte sequence is valid for this struct.
>>  unsafe impl FromBytes for FalconAppifHdrV1 {}
>>  
>>  #[repr(C, packed)]
>> @@ -44,7 +44,7 @@ struct FalconAppifV1 {
>>      id: u32,
>>      dmem_base: u32,
>>  }
>> -// SAFETY: any byte sequence is valid for this struct.
>> +// SAFETY: Any byte sequence is valid for this struct.
>>  unsafe impl FromBytes for FalconAppifV1 {}
>>  
>>  #[derive(Debug)]
>> @@ -68,8 +68,10 @@ struct FalconAppifDmemmapperV3 {
>>      ucode_cmd_mask1: u32,
>>      multi_tgt_tbl: u32,
>>  }
>> -// SAFETY: any byte sequence is valid for this struct.
>> +// SAFETY: Any byte sequence is valid for this struct.
> 
> I appreciate the capitalization, but these changes are a bit
> distracting. :) If you absolutely want to do this, let it be its own
> patch so the current one stays focused on what it actually does.
> 
>>  unsafe impl FromBytes for FalconAppifDmemmapperV3 {}
>> +// SAFETY: This struct doesn't contain unitialized bytes and doesn't have interior mutability.
> 
> Typo: s/unitialized/uninitialized (and in other comments as well).
> 
I will move the capitalization to another patch and fix the typo.

> Otherwise this looks ok - it doesn't apply cleanly on drm-rust-next
> though, could you rebase for the next version?

About this, I was basing myself on nova-next [1]. I will rebase on top
of drm-rust-next for the next version.


Link: https://gitlab.freedesktop.org/drm/nova [1]
Link:
https://gitlab.freedesktop.org/drm/rust/kernel/-/tree/drm-rust-next [2]

> 
> Thanks for the cleanup!

Thanks to you for the reviews and the patience!