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Message-ID: <0B70DC73-6796-4114-9C2B-6B1B9AD560A5@nvidia.com> Date: Mon, 20 Oct 2025 19:48:32 +0000 From: Joel Fernandes <joelagnelf@...dia.com> To: John Hubbard <jhubbard@...dia.com> CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "rust-for-linux@...r.kernel.org" <rust-for-linux@...r.kernel.org>, "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, "dakr@...nel.org" <dakr@...nel.org>, Alexandre Courbot <acourbot@...dia.com>, 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>, "bjorn3_gh@...tonmail.com" <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>, Timur Tabi <ttabi@...dia.com>, "joel@...lfernandes.org" <joel@...lfernandes.org>, Elle Rhumsaa <elle@...thered-steel.dev>, Daniel Almeida <daniel.almeida@...labora.com>, "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org> Subject: Re: [PATCH 4/7] docs: gpu: nova-core: Document the PRAMIN aperture mechanism > On Oct 20, 2025, at 3:36 PM, John Hubbard <jhubbard@...dia.com> wrote: > > On 10/20/25 11:55 AM, Joel Fernandes wrote: > ...> +Logically, the PRAMIN aperture mechanism is implemented by the GPU's PBUS (PCIe Bus Controller Unit) >> +and provides a CPU-accessible window into VRAM through the PCIe interface:: >> + >> + +-----------------+ PCIe +------------------------------+ >> + | CPU |<----------->| GPU | >> + +-----------------+ | | >> + | +----------------------+ | >> + | | PBUS | | >> + | | (Bus Controller) | | >> + | | | | >> + | | +--------------.<------------ (window always starts at >> + | | | PRAMIN | | | BAR0 + 0x700000) > > Quick question: does "window always starts at" actually mean "windows > is always initialized to" ? Or something else? It means start of the 1MB window (offset 0) is accessed from the BAR at that location. Thanks. > > > thanks, > -- > John Hubbard > >> + | | | Window | | | >> + | | | (1MB) | | | >> + | | +--------------+ | | >> + | | | | | >> + | +---------|------------+ | >> + | | | >> + | v | >> + | .----------------------.<------------ (Program PRAMIN to any >> + | | VRAM | | 64KB VRAM physical boundary) >> + | | (Several GBs) | | >> + | | | | >> + | | FB[0x000000000000] | | >> + | | ... | | >> + | | FB[0x7FFFFFFFFFF] | | >> + | +----------------------+ | >> + +------------------------------+ >> + >> +PBUS (PCIe Bus Controller) among other things is responsible in the GPU for handling MMIO >> +accesses to the BAR registers. >> + >> +PRAMIN Window Operation >> +======================= >> + >> +The PRAMIN window provides a 1MB sliding aperture that can be repositioned over >> +the entire VRAM address space using the NV_PBUS_BAR0_WINDOW register. >> + >> +Window Control Mechanism >> +------------------------- >> + >> +The window position is controlled via the PBUS BAR0_WINDOW register:: >> + >> + NV_PBUS_BAR0_WINDOW Register >> + +-----+-----+--------------------------------------+ >> + |31-26|25-24| 23-0 | >> + | |TARG | BASE_ADDR | >> + | | ET | (bits 39:16 of VRAM address) | >> + +-----+-----+--------------------------------------+ >> + >> + TARGET field values: >> + - 0x0: VID_MEM (Video Memory / VRAM) >> + - 0x1: SYS_MEM_COHERENT (Coherent system memory) >> + - 0x2: SYS_MEM_NONCOHERENT (Non-coherent system memory) >> + >> +64KB Alignment Requirement >> +--------------------------- >> + >> +The PRAMIN window must be aligned to 64KB boundaries in VRAM. This is enforced >> +by the BASE_ADDR field representing bits [39:16] of the target address:: >> + >> + VRAM Address Calculation: >> + actual_vram_addr = (BASE_ADDR << 16) + pramin_offset >> + Where: >> + - BASE_ADDR: 24-bit value from NV_PBUS_BAR0_WINDOW[23:0] >> + - pramin_offset: 20-bit offset within PRAMIN window [0x00000-0xFFFFF] >> + Example Window Positioning: >> + +---------------------------------------------------------+ >> + | VRAM Space | >> + | | >> + | 0x000000000 +-----------------+ <-- 64KB aligned | >> + | | PRAMIN Window | | >> + | | (1MB) | | >> + | 0x0000FFFFF +-----------------+ | >> + | | >> + | | ^ | >> + | | | Window can slide | >> + | v | to any 64KB boundary | >> + | | >> + | 0x123400000 +-----------------+ <-- 64KB aligned | >> + | | PRAMIN Window | | >> + | | (1MB) | | >> + | 0x1234FFFFF +-----------------+ | >> + | | >> + | ... | >> + | | >> + | 0x7FFFF0000 +-----------------+ <-- 64KB aligned | >> + | | PRAMIN Window | | >> + | | (1MB) | | >> + | 0x7FFFFFFFF +-----------------+ | >> + +---------------------------------------------------------+ >> diff --git a/Documentation/gpu/nova/index.rst b/Documentation/gpu/nova/index.rst >> index 46302daace34..e77d3ee336a4 100644 >> --- a/Documentation/gpu/nova/index.rst >> +++ b/Documentation/gpu/nova/index.rst >> @@ -33,3 +33,4 @@ vGPU manager VFIO driver and the nova-drm driver. >> core/fwsec >> core/falcon >> core/msgq >> + core/pramin > >
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