[PATCH v2 1/2] gpu: nova-core: declare unlimited DMA max segment size
From: Matteo Kloiber <hidden>
Date: 2026-09-13 21:13:33
Also in:
dri-devel, driver-core, lkml, rust-for-linux
Subsystem:
core driver for nvidia gpus [rust], drm drivers, drm drivers and common infrastructure [rust], the rest · Maintainers:
Danilo Krummrich, Alexandre Courbot, David Airlie, Simona Vetter, Alice Ryhl, Linus Torvalds
The PCI default max_seg_size is 64 KiB. nova-core never raises it, so mapping the GSP firmware image (~60 MiB) as a scatter-gather table triggers a DMA-API debug warning when contiguous pages coalesce into segments that exceed the default: DMA-API: nova-core 0000:00:03.0: mapping sg segment longer than device claims to support [len=62914560] [max=65536] CONFIG_DMA_API_DEBUG=y is required to see this warning. Assisted-by: LLM Signed-off-by: Matteo Kloiber <redacted> --- drivers/gpu/nova-core/gpu.rs | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
index fd1414004dd0..edc0207c01a0 100644
--- a/drivers/gpu/nova-core/gpu.rs
+++ b/drivers/gpu/nova-core/gpu.rs@@ -343,6 +343,13 @@ pub(crate) fn new<'a>( // still constructing it, so no concurrent DMA allocations can exist. unsafe { pdev.dma_set_mask_and_coherent(dma_mask)? }; + // Nova walks SG segments to build page tables, so their length is + // irrelevant to the device. + // + // SAFETY: `Gpu` owns all DMA allocations for this device, and we are + // still constructing it, so no concurrent DMA allocations can exist. + unsafe { pdev.dma_set_max_seg_size(u32::MAX) }; + hal.wait_gfw_boot_completion(bar) .inspect_err(|_| dev_err!(dev, "GFW boot did not complete\n"))?; },
--
2.51.2