Re: [PATCH v3 16/19] nova-core: Add support for VBIOS ucode extraction for boot

[Joel Fernandes <joelagnelf@nvidia.com>]

On 5/20/2025 11:01 AM, Danilo Krummrich wrote:
> On Tue, May 20, 2025 at 09:43:42AM -0400, Joel Fernandes wrote:
>> On 5/20/2025 5:30 AM, Danilo Krummrich wrote:
>>> On Tue, May 20, 2025 at 03:55:06AM -0400, Joel Fernandes wrote:
>>>> On 5/13/2025 1:19 PM, Danilo Krummrich wrote:
>>>>> On Wed, May 07, 2025 at 10:52:43PM +0900, Alexandre Courbot wrote:
>>
>> So the code here now looks like the below, definitely better, thanks! :
>>
>>             if let (Some(second_ref), Some(first), Some(pci_at)) =
>>                 (second.as_mut(), first_fwsec_image, pci_at_image)
>>             {
>>                 second_ref
>>                     .setup_falcon_data(pdev, &pci_at, &first)
>>                     .inspect_err(|e| {
>>                         dev_err!(..)
>>                     })?;
>>                 Ok(Vbios { fwsec_image: second.take().ok_or(EINVAL)? })
>>             } else {
>>                 dev_err!(
>>                     pdev.as_ref(),
>>                     "Missing required images for falcon data setup, skipping\n"
>>                 );
>>                 Err(EINVAL)
>>             }
> 
> Sorry, my code-snipped was incorrect indeed. Let me paste what I actually
> intended (and this time properly compile checked) and should be even better:
> 
> 	if let (Some(mut second), Some(first), Some(pci_at)) =
> 	    (second_fwsec_image, first_fwsec_image, pci_at_image)
> 	{
> 	    second
> 	        .setup_falcon_data(pdev, &pci_at, &first)
> 	        .inspect_err(|e| {
> 	            dev_err!(pdev.as_ref(), "Falcon data setup failed: {:?}\n", e)
> 	        })?;
> 	
> 	    Ok(Vbios(second))
> 	} else {
> 	    dev_err!(
> 	        pdev.as_ref(),
> 	        "Missing required images for falcon data setup, skipping\n"
> 	    );
> 	
> 	    Err(EINVAL)
> 	}
> 
> So, with this second is the actual value and not just a reference. :)
> 
> And the methods can become:
> 
> 	pub(crate) fn fwsec_header(&self, pdev: &device::Device) -> Result<&FalconUCodeDescV3> {
> 	    self.0.fwsec_header(pdev)
> 	}
> 	
> 	pub(crate) fn fwsec_ucode(&self, pdev: &device::Device) -> Result<&[u8]> {
> 	    self.0.fwsec_ucode(pdev, self.fwsec_header(pdev)?)
> 	}
> 	
> 	pub(crate) fn fwsec_sigs(&self, pdev: &device::Device) -> Result<&[u8]> {
> 	    self.0.fwsec_sigs(pdev, self.fwsec_header(pdev)?)
> 	}

I made this change and it LGTM. Thanks! I did not do the '.0' though since I
want to keep the readability, lets see in the next revision if that looks good.

>>> In general, I feel like a lot of those Option come from a programming pattern
>>> that is very common in C, i.e. allocate a structure (stack or heap) and then
>>> initialize its fields.
>>>
>>> In Rust you should aim to initialize all the fields of a structure when you
>>> create the instance. Option as a return type of a function is common, but it's
>>> always a bit suspicious when there is an Option field in a struct.
>>
>> I looked into it, I could not git rid of those ones because we need to
>> initialize in the "impl TryFrom<BiosImageBase> for BiosImage {"
>>
>>             0xE0 => Ok(BiosImage::FwSec(FwSecBiosImage {
>>                 base,
>>                 falcon_data_offset: None,
>>                 pmu_lookup_table: None,
>>                 falcon_ucode_offset: None,
>>             })),
>>
>> And these fields will not be determined until much later, because as is the case
>> with the earlier example, these fields cannot be determined until all the images
>> are parsed.
> 
> You should not use TryFrom, but instead use a normal constructor, such as
> 
> 	BiosImage::new(base_bios_image)
> 
> and do the parsing within this constructor.
> 
> If you want a helper type with Options while parsing that's totally fine, but
> the final result can clearly be without Options. For instance:
> 
> 	struct Data {
> 	   image: KVec<u8>,
> 	}
> 
> 	impl Data {
> 	   fn new() -> Result<Self> {
> 	      let parser = DataParser::new();
> 
> 	      Self { image: parser.parse()? }
> 	   }
> 
> 	   fn load_image(&self) {
> 	      ...
> 	   }
> 	}
> 
> 	struct DataParser {
> 	   // Only some images have a checksum.
> 	   checksum: Option<u64>,
> 	   // Some images have an extra offset.
> 	   offset: Option<u64>,
> 	   // Some images need to be patched.
> 	   patch: Option<KVec<u8>>,
> 	   image: KVec<u8>,
> 	}
> 
> 	impl DataParser {
> 	   fn new() -> Self {
> 	      Self {
> 	         checksum: None,
> 	         offset: None,
> 	         patch: None,
> 	         bytes: KVec::new(),
> 	      }
> 	   }
> 
> 	   fn parse(self) -> Result<KVec<u8>> {
> 	      // Fetch all the required data.
> 	      self.fetch_checksum()?;
> 	      self.fetch_offset()?;
> 	      self.fetch_patch()?;
> 	      self.fetch_byes()?;
> 
> 	      // Doesn't do anything if `checksum == None`.
> 	      self.validate_checksum()?;
> 
> 	      // Doesn't do anything if `offset == None`.
> 	      self.apply_offset()?;
> 
> 	      // Doesn't do anything if `patch == None`.
> 	      self.apply_patch()?;
> 
> 	      // Return the final image.
> 	      self.image
> 	   }
> 	}
> 
> I think the pattern here is the same, but in this example you keep working with
> the DataParser, instead of a new instance of Data.

I think this would be a fundamental rewrite of the patch. I am Ok with looking
into it as a future item, but right now I am not sure if it justifies not using
Option for these few. There's a lot of immediate work we have to do for boot,
lets please not block the patch on just this if that's Ok with you. If you want,
I could add a TODO here.

thanks,

 - Joel