Re: [PATCH v4 08/33] gpu: nova-core: set DMA mask width based on GPU architecture

John Hubbard
2026-02-12T02:07:22Z

On 2/11/26 2:28 AM, Danilo Krummrich wrote:
> On Tue Feb 10, 2026 at 3:45 AM CET, John Hubbard wrote:
>> This removes a "TODO" item in the code, which was hardcoded to work on
>> Ampere and Ada GPUs. Hopper/Blackwell+ have a larger width, so do an
>> early read of boot42, in order to pick the correct value.
>>
>> Cc: Gary Guo <gary@garyguo.net>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>> ---
>> drivers/gpu/nova-core/driver.rs | 33 ++++++++++++++--------------
>> drivers/gpu/nova-core/gpu.rs | 38 ++++++++++++++++++++++++---------
>> 2 files changed, 44 insertions(+), 27 deletions(-)
>>
>> diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
>> index e39885c0d5ca..4ff07b643db6 100644
>> --- a/drivers/gpu/nova-core/driver.rs
>> +++ b/drivers/gpu/nova-core/driver.rs
>> @@ -5,7 +5,6 @@
>> device::Core,
>> devres::Devres,
>> dma::Device,
>> - dma::DmaMask,
>> pci,
>> pci::{
>> Class,
>> @@ -17,7 +16,10 @@
>> sync::Arc, //
>> };
>>
>> -use crate::gpu::Gpu;
>> +use crate::gpu::{
>> + Gpu,
>> + Spec, //
>> +};
>>
>> #[pin_data]
>> pub(crate) struct NovaCore {
>> @@ -29,14 +31,6 @@ pub(crate) struct NovaCore {
>>
>> const BAR0_SIZE: usize = SZ_16M;
>>
>> -// For now we only support Ampere which can use up to 47-bit DMA addresses.
>> -//
>> -// TODO: Add an abstraction for this to support newer GPUs which may support
>> -// larger DMA addresses. Limiting these GPUs to smaller address widths won't
>> -// have any adverse affects, unless installed on systems which require larger
>> -// DMA addresses. These systems should be quite rare.
>> -const GPU_DMA_BITS: u32 = 47;
>> -
>> pub(crate) type Bar0 = pci::Bar<BAR0_SIZE>;
>>
>> kernel::pci_device_table!(
>> @@ -75,18 +69,23 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<Self, E
>> pdev.enable_device_mem()?;
>> pdev.set_master();
>>
>> - // SAFETY: No concurrent DMA allocations or mappings can be made because
>> - // the device is still being probed and therefore isn't being used by
>> - // other threads of execution.
>> - unsafe { pdev.dma_set_mask_and_coherent(DmaMask::new::<GPU_DMA_BITS>())? };
>> -
>> - let bar = Arc::pin_init(
>
> Spurious rename.

Reverted.

>
>> + let devres_bar = Arc::pin_init(
>> pdev.iomap_region_sized::<BAR0_SIZE>(0, c"nova-core/bar0"),
>> GFP_KERNEL,
>> )?;
>>
>> + // Read the GPU spec early to determine the correct DMA address width.
>
> Hm.. we should move the dma_set_mask_and_coherent() call into Gpu::new(), so all
> GPU specific initialization remains in the constructor of Gpu.

Makes sense, done.

>
>> + // Hopper/Blackwell+ support 52-bit DMA addresses, earlier architectures use 47-bit.
>
> I'd move this down to the dma_set_mask_and_coherent() call, or maybe just remove
> it as well, since we have the very same comment for Architecture::dma_mask().

Done.

>
>> + let spec = Spec::new(pdev.as_ref(), devres_bar.access(pdev.as_ref())?)?;
>> + dev_info!(pdev.as_ref(), "NVIDIA ({})\n", spec);
>
> This re-introduces pdev.as_ref().

Fixed.

Very helpful, thanks!

thanks,
--
John Hubbard

>
>> +
>> + // SAFETY: No concurrent DMA allocations or mappings can be made because
>> + // the device is still being probed and therefore isn't being used by
>> + // other threads of execution.
>> + unsafe { pdev.dma_set_mask_and_coherent(spec.chipset().arch().dma_mask())? };
>> +
>> Ok(try_pin_init!(Self {
>> - gpu <- Gpu::new(pdev, bar.clone(), bar.access(pdev.as_ref())?),
>> + gpu <- Gpu::new(pdev, devres_bar.clone(), devres_bar.access(pdev.as_ref())?, spec),
>> _reg <- auxiliary::Registration::new(
>> pdev.as_ref(),
>> c"nova-drm",