linux-kernel - Re: [PATCH 4/7] docs: gpu: nova-core: Document the PRAMIN aperture mechanism

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Message-ID: <c65d6318-0de4-46cf-8f70-8a1c4aba179a@nvidia.com>
Date: Mon, 20 Oct 2025 13:42:13 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Joel Fernandes <joelagnelf@...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>,
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 "dakr@...nel.org" <dakr@...nel.org>, Alexandre Courbot
 <acourbot@...dia.com>, Alistair Popple <apopple@...dia.com>,
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 "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 10/20/25 12:48 PM, Joel Fernandes wrote:
> 
> 
>> 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.
> 
OK, yes. May I suggest this slightly tweaked wording:

   (window into VRAM starts at BAR0 + 0x700000)

? 

This avoids "always" (because HW may change someday), and also
gives a subtly stronger hint about how this is laid out.



thanks,
-- 
John Hubbard