linux-kernel - [PATCH v5 01/14] gpu: nova-core: Set correct DMA mask

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Message-ID: <20251013062041.1639529-2-apopple@nvidia.com>
Date: Mon, 13 Oct 2025 17:20:27 +1100
From: Alistair Popple <apopple@...dia.com>
To: rust-for-linux@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	dakr@...nel.org,
	acourbot@...dia.com
Cc: Alistair Popple <apopple@...dia.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	John Hubbard <jhubbard@...dia.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Timur Tabi <ttabi@...dia.com>,
	linux-kernel@...r.kernel.org,
	nouveau@...ts.freedesktop.org
Subject: [PATCH v5 01/14] gpu: nova-core: Set correct DMA mask

Set the correct DMA mask. Without this DMA will fail on some setups.

Signed-off-by: Alistair Popple <apopple@...dia.com>

---

Changes for v5:
 - Update SAFETY comment for dma_set_mask_and_coherent()
 - Add TODO for using different masks when we support more GPU models

Changes for v4:
 - Use a const (GPU_DMA_BITS) instead of a magic number

Changes for v2:
 - Update DMA mask to correct value for Ampere/Turing (47 bits)
---
 drivers/gpu/nova-core/driver.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
index edc72052e27a..2407d0ab15e2 100644
--- a/drivers/gpu/nova-core/driver.rs
+++ b/drivers/gpu/nova-core/driver.rs
@@ -3,6 +3,8 @@
 use kernel::{
     auxiliary, c_str,
     device::Core,
+    dma::Device,
+    dma::DmaMask,
     pci,
     pci::{Class, ClassMask, Vendor},
     prelude::*,
@@ -20,6 +22,15 @@ 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!(
@@ -57,6 +68,11 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self
         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 devres_bar = Arc::pin_init(
             pdev.iomap_region_sized::<BAR0_SIZE>(0, c_str!("nova-core/bar0")),
             GFP_KERNEL,
-- 
2.50.1