Re: [PATCH] gpu: nova-core: Use bar1_resource_index() in NovaCoreApi::bar1_size()

["Alexandre Courbot" <acourbot@nvidia.com>]

On Thu Oct 1, 2026 at 9:56 AM JST, Alistair Popple wrote:
> bar1_size() reports the length of PCI resource 1 as the size of BAR1.
> That is only correct when BAR0 is a 32-bit BAR. On Blackwell, and on some
> Ampere GA100 and Hopper SKUs, BAR0 is 64-bit and takes resource slots 0
> and 1, pushing BAR1 to slot 2. Slot 1 is then the upper half of BAR0
> rather than a BAR of its own, so NOVA_GETPARAM_VRAM_BAR_SIZE reports the
> wrong size on those GPUs.
>
> Probe handles this with the new bar1_resource_index(), which it uses to
> map BAR1, so use the same lookup here.
>
> Fixes: 7edc491f6fca ("drm: nova: Use nova-core to read VRAM_BAR_SIZE parameter")
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>
> ---
>
> Danilo,
>
> Not sure how you want to take this, you could either take it as a
> standalone patch or fold it into my series as the pre-requisite change
> that introduced bar1_resource_index() 159427b21352 ("gpu: nova-core: mm:
> Add BAR1 user interface") comes before my series in drm-rust-next.
>
>  - Alistair
> ---
>  drivers/gpu/nova-core/api.rs | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/nova-core/api.rs b/drivers/gpu/nova-core/api.rs
> index f02c6c7c7e51..cc1d936b002c 100644
> --- a/drivers/gpu/nova-core/api.rs
> +++ b/drivers/gpu/nova-core/api.rs
> @@ -44,7 +44,9 @@ pub fn spec(&self) -> &Spec {
>      /// Returns the size of the PCIe BAR used for accessing VRAM, typically
>      /// BAR1.
>      pub fn bar1_size(&self) -> Result<u64> {
> -        self.pdev.resource_len(1)
> +        let bar1 = crate::driver::bar1_resource_index(self.pdev)?;
> +
> +        self.pdev.resource_len(bar1)

I guess at some point we will want an iterator on `pci::Device` that
returns a `BarInfo` type or something? Zhi has some similar logic in his
SR-IOV series (method `vf_bars` of [1]) and this seems to be a common
mistake code makes when iterating BARs.

Just an idea for a future patch, this one is of course correct.

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>

[1] https://lore.kernel.org/all/20260906060404.3336193-2-zhiw@nvidia.com/