linux-kernel - Re: [PATCH v3 14/14] gpu: nova-core: gsp: Retrieve GSP static info to gather GPU information

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Message-ID: <f36dc492-507b-489c-8609-6a760526a371@nvidia.com>
Date: Wed, 12 Nov 2025 15:22:43 -0500
From: Joel Fernandes <joelagnelf@...dia.com>
To: Lyude Paul <lyude@...hat.com>, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 dakr@...nel.org, acourbot@...dia.com
Cc: Alistair Popple <apopple@...dia.com>, Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>, 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>,
 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>, Timur Tabi <ttabi@...dia.com>,
 joel@...lfernandes.org, Daniel Almeida <daniel.almeida@...labora.com>,
 nouveau@...ts.freedesktop.org
Subject: Re: [PATCH v3 14/14] gpu: nova-core: gsp: Retrieve GSP static info to
 gather GPU information

On 11/11/2025 5:02 PM, Lyude Paul wrote:
[...]

>> +#[repr(C)]
>> +#[derive(Debug, Copy, Clone)]
>> +pub struct GspStaticConfigInfo_t {
>> +    pub grCapsBits: [u8_; 23usize],
>> +    pub gidInfo: NV2080_CTRL_GPU_GET_GID_INFO_PARAMS,
>> +    pub SKUInfo: NV2080_CTRL_BIOS_GET_SKU_INFO_PARAMS,
>> +    pub fbRegionInfoParams: NV2080_CTRL_CMD_FB_GET_FB_REGION_INFO_PARAMS,
>> +    pub sriovCaps: NV0080_CTRL_GPU_GET_SRIOV_CAPS_PARAMS,
>> +    pub sriovMaxGfid: u32_,
>> +    pub engineCaps: [u32_; 3usize],
>> +    pub poisonFuseEnabled: u8_,
>> +    pub fb_length: u64_,
>> +    pub fbio_mask: u64_,
>> +    pub fb_bus_width: u32_,
>> +    pub fb_ram_type: u32_,
>> +    pub fbp_mask: u64_,
>> +    pub l2_cache_size: u32_,
>> +    pub gpuNameString: [u8_; 64usize],
>> +    pub gpuShortNameString: [u8_; 64usize],

[...]

>> +mod util;
>>  mod vbios;
>>  
>>  pub(crate) const MODULE_NAME: &kernel::str::CStr = <LocalModule as kernel::ModuleMetadata>::NAME;
>> diff --git a/drivers/gpu/nova-core/util.rs b/drivers/gpu/nova-core/util.rs
>> new file mode 100644
>> index 000000000000..f1a4dea44c10
>> --- /dev/null
>> +++ b/drivers/gpu/nova-core/util.rs
>> @@ -0,0 +1,16 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +/// Converts a null-terminated byte array to a string slice.
>> +///
>> +/// Returns "invalid" if the bytes are not valid UTF-8 or not null-terminated.
>> +pub(crate) fn str_from_null_terminated(bytes: &[u8]) -> &str {
>> +    use kernel::str::CStr;
>> +
>> +    // Find the first null byte, then create a slice that includes it.
>> +    bytes
>> +        .iter()
>> +        .position(|&b| b == 0)
>> +        .and_then(|null_pos| CStr::from_bytes_with_nul(&bytes[..=null_pos]).ok())
>> +        .and_then(|cstr| cstr.to_str().ok())
>> +        .unwrap_or("invalid")
> 
> I feel like I'm missing something obvious here so excuse me if I am. But if
> CStr::from_bytes_with_nul is already scanning the string for a NULL byte, why
> do we need to do iter().position(|&b| b == 0)?

It is because the .get() above could potentially return an entire buffer with
no-null termintaor, as unlikely as that might be. In this case the
`.unwrap_or(msg.gpuNameString.len() - 1),` bit will execute returning 63 as the
length of the buffer space is 64 bytes. `CStr::from_bytes_with_nul()` will then
separately look for the NULL and fail into returning "invalid" as the string.

So mainly, the redundant `.position()` call is it is to handle the failure case.

But you found some duplicated code here! Let me go ahead and just call this
function instead of open coding it.

Thanks.