Re: [PATCH 2/7] gpu: nova-core: place the generic bootloader at the top of IMEM

[Eliot Courtney]

On Tue Nov 3, 2026 at 7:22 PM JST, Alexandre Courbot wrote:
> From: John Hubbard <jhubbard@xxxxxxxxxx>
>
> The generic bootloader was loaded right below the first 64 KiB of IMEM,
> on the assumption that every falcon it runs on has a 64 KiB IMEM. The
> r000 load-and-execute bootloader event can name any image for it to
> load, and the bootloader must then sit above the blocks that the image
> occupies, that is, in the last blocks of IMEM, regardless of its size.
>
> Place the bootloader at the top of the falcon's IMEM, using the IMEM
> size that the HWCFG register reports, instead of assuming a 64 KiB IMEM.
>
> Assisted-by: LLM
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> Reviewed-by: Timur Tabi <ttabi@xxxxxxxxxx>
> Reviewed-by: Zhi Wang <zhiw@xxxxxxxxxx>
> [acourbot: split out of the patch separating the bootloader from FWSEC;
>  convert the IMEM size with usize::from()]
> Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
> ---
>  drivers/gpu/nova-core/falcon.rs                    |  7 +++++++
>  drivers/gpu/nova-core/firmware/fwsec/bootloader.rs |  3 ++-
>  drivers/gpu/nova-core/firmware/gen_bootloader.rs   | 23 +++++++++++++---------
>  drivers/gpu/nova-core/gsp/hal/tu102.rs             |  6 ++++--
>  drivers/gpu/nova-core/regs.rs                      |  5 +++++
>  5 files changed, 32 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/falcon.rs b/drivers/gpu/nova-core/falcon.rs
> index 0b377bd6524a..1bceb38c33c6 100644
> --- a/drivers/gpu/nova-core/falcon.rs
> +++ b/drivers/gpu/nova-core/falcon.rs
> @@ -382,6 +382,13 @@ pub(crate) fn new(
>          })
>      }
>  
> +    /// Returns the size of this falcon's IMEM in bytes.
> +    pub(crate) fn imem_size(&self) -> usize {
> +        let blocks = usize::from(self.pfalcon.read(regs::NV_PFALCON_FALCON_HWCFG).imem_size());
> +
> +        blocks * MEM_BLOCK_ALIGNMENT
> +    }
> +
>      /// Resets DMA-related registers.
>      pub(crate) fn dma_reset(&self) {
>          self.pfalcon.update(regs::NV_PFALCON_FBIF_CTL, |v| {
> diff --git a/drivers/gpu/nova-core/firmware/fwsec/bootloader.rs b/drivers/gpu/nova-core/firmware/fwsec/bootloader.rs
> index 59f57714fcfb..3943948d74bc 100644
> --- a/drivers/gpu/nova-core/firmware/fwsec/bootloader.rs
> +++ b/drivers/gpu/nova-core/firmware/fwsec/bootloader.rs
> @@ -108,8 +108,9 @@ pub(crate) fn new(

nit: docs on `GenericBootloader::new` and `FwsecFirmwareWithBl::new`
need updating
> -    pub(crate) fn new(dev: &device::Device<device::Bound>, chipset: Chipset) -> Result<Self> {
> +    pub(crate) fn new(
> +        dev: &device::Device<device::Bound>,
> +        chipset: Chipset,
> +        falcon: &Falcon<'_, Gsp>,
> +    ) -> Result<Self> {
>          let fw = request_tlv(dev, chipset, "gen_bootloader")?;
>          let tlv = Tlv::new(fw.data())?;
>          dev_dbg!(
> @@ -68,9 +73,9 @@ pub(crate) fn new(dev: &device::Device<device::Bound>, chipset: Chipset) -> Resu
>              ucode
>          };
>  
> -        // The bootloader's code must be loaded in the area right below the first 64K of IMEM.
> -        const BOOTLOADER_LOAD_CEILING: usize = sizes::SZ_64K;
> -        let imem_dst_start = BOOTLOADER_LOAD_CEILING
> +        // The top of IMEM, above the blocks that the bootloader loads the image into.
> +        let imem_dst_start = falcon
> +            .imem_size()
>              .checked_sub(ucode.len())
>              .ok_or(EOVERFLOW)?;

`imem_size` is 8:0 (so 9 bits), and multiplied by 256. So it can be max
~2^17. Then we subtract off ucode.len() and do u16::try_from, so that
could fail. I don't know if any real hardware actually hits this though.
This value (`imem_dst_start`) eventually gets written into
NV_PFALCON_FALCON_IMEMC::offs which is 15:0 in nova. According to openrm
though, it's 15:0 for turing, and after that it's 23:0. So maybe worth
checking (then we'd widen `imem_dst_start` etc to u32). I think it
probably 'just works' fine to switch to u32 and change
NV_PFALCON_FALCON_IMEMC::offs to 23:0, even for turing, and would be the
same behaviour as nouveau afaict.