Re: [PATCH] gpu: nova-core: depend on CONFIG_64BIT

["Danilo Krummrich" <dakr@kernel.org>]

On Fri Aug 29, 2025 at 12:39 AM CEST, Danilo Krummrich wrote:
> If built on architectures with CONFIG_ARCH_DMA_ADDR_T_64BIT=y nova-core
> produces that following build failures:
>
>     error[E0308]: mismatched types
>       --> drivers/gpu/nova-core/fb.rs:49:59
>        |
>     49 |         hal::fb_hal(chipset).write_sysmem_flush_page(bar, page.dma_handle())?;
>        |                              -----------------------      ^^^^^^^^^^^^^^^^^ expected `u64`, found `u32`
>        |                              |
>        |                              arguments to this method are incorrect
>        |
>     note: method defined here
>       --> drivers/gpu/nova-core/fb/hal.rs:19:8
>        |
>     19 |     fn write_sysmem_flush_page(&self, bar: &Bar0, addr: u64) -> Result;
>        |        ^^^^^^^^^^^^^^^^^^^^^^^
>     help: you can convert a `u32` to a `u64`
>        |
>     49 |         hal::fb_hal(chipset).write_sysmem_flush_page(bar, page.dma_handle().into())?;
>        |                                                                            +++++++
>
>     error[E0308]: mismatched types
>       --> drivers/gpu/nova-core/fb.rs:65:47
>        |
>     65 |         if hal.read_sysmem_flush_page(bar) == self.page.dma_handle() {
>        |            -------------------------------    ^^^^^^^^^^^^^^^^^^^^^^ expected `u64`, found `u32`
>        |            |
>        |            expected because this is `u64`
>        |
>     help: you can convert a `u32` to a `u64`
>        |
>     65 |         if hal.read_sysmem_flush_page(bar) == self.page.dma_handle().into() {
>        |                                                                     +++++++
>
>     error: this arithmetic operation will overflow
>        --> drivers/gpu/nova-core/falcon.rs:469:23
>         |
>     469 |             .set_base((dma_start >> 40) as u16)
>         |                       ^^^^^^^^^^^^^^^^^ attempt to shift right by `40_i32`, which would overflow
>         |
>         = note: `#[deny(arithmetic_overflow)]` on by default
>
> This is due to the code making assumptions on the width of dma_addr_t to
> be 64 bit.
>
> While this could technically be handled, it is rather painful to deal
> with, as the following example illustrates:
>
> 	pub(super) fn read_sysmem_flush_page_ga100(bar: &Bar0) -> DmaAddress {
> 	    let addr = u64::from(regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR::read(bar).adr_39_08())
> 	        << FLUSH_SYSMEM_ADDR_SHIFT
> 	        | u64::from(regs::NV_PFB_NISO_FLUSH_SYSMEM_ADDR_HI::read(bar).adr_63_40())
> 	            << FLUSH_SYSMEM_ADDR_SHIFT_HI;
>
> 	    addr.try_into().unwrap_or_else(|_| {
> 	        kernel::warn_on!(true);
>
> 	        0
> 	    })
> 	}
>
> At the same time there's not much value for nova-core to support 32-bit,
> given that the supported GPU architectures are Turing and later, hence
> depend on CONFIG_64BIT.
>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Reported-by: Miguel Ojeda <ojeda@kernel.org>
> Closes: https://lore.kernel.org/lkml/20250828160247.37492-1-ojeda@kernel.org/
> Fixes: 6554ad65b589 ("gpu: nova-core: register sysmem flush page")
> Fixes: 69f5cd67ce41 ("gpu: nova-core: add falcon register definitions and base code")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Applied to drm-rust-fixes, thanks!