[PATCH v2 1/2] gpu: nova-core: declare unlimited DMA max segment size

[Matteo Kloiber <kernel@matt3o12.de>]

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 <kernel@matt3o12.de>
---
 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