linux-kernel - Re: [PATCH v4 16/20] nova-core: Add support for VBIOS ucode extraction for boot

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Message-ID: <5e9f52d0-d2ad-4d25-a481-22f8c6055021@nvidia.com>
Date: Wed, 4 Jun 2025 14:23:30 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>,
 Alexandre Courbot <acourbot@...dia.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 John Hubbard <jhubbard@...dia.com>, Ben Skeggs <bskeggs@...dia.com>,
 Timur Tabi <ttabi@...dia.com>, Alistair Popple <apopple@...dia.com>,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
 nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 Shirish Baskaran <sbaskaran@...dia.com>
Subject: Re: [PATCH v4 16/20] nova-core: Add support for VBIOS ucode
 extraction for boot



On 6/2/2025 9:33 AM, Danilo Krummrich wrote:
>> +    /// Try to find NPDE in the data, the NPDE is right after the PCIR.
>> +    fn find_in_data(
>> +        pdev: &pci::Device,
>> +        data: &[u8],
>> +        rom_header: &PciRomHeader,
>> +        pcir: &PcirStruct,
>> +    ) -> Option<Self> {
>> +        // Calculate the offset where NPDE might be located
>> +        // NPDE should be right after the PCIR structure, aligned to 16 bytes
>> +        let pcir_offset = rom_header.pci_data_struct_offset as usize;
>> +        let npde_start = (pcir_offset + pcir.pci_data_struct_len as usize + 0x0F) & !0x0F;
>
> What's this magic offset and mask?
> 

Oh, hmm. I had a comment on that above though ("NPDE should be right after the
PCIR structure, aligned to 16 bytes"), does that suffice? I could move the
comment further down.

>> +
>> +        // Check if we have enough data
>> +        if npde_start + 11 > data.len() {
>
> '+ 11'?

Good point, I replaced this and the above with core::mem::size_of::<Self>().

> 
>> +            dev_err!(pdev.as_ref(), "Not enough data for NPDE\n");
> BiosImageBase declares this as "NVIDIA PCI Data Extension (optional)". If it's
> really optional, why is this an error?
> 
>> +            return None;
>> +        }
>> +
>> +        // Try to create NPDE from the data
>> +        NpdeStruct::new(pdev, &data[npde_start..])
>> +            .inspect_err(|e| {
>> +                dev_err!(pdev.as_ref(), "Error creating NpdeStruct: {:?}\n", e);
>> +            })
>> +            .ok()
>
> So, this returns None if it's a real error. This indicates that the return type
> should just be Result<Option<Self>>.

I made NpdeStruct::new() return Option only for next revision since NPDE is
optional.

thanks,

 - Joel