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

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Message-ID: <32c266bc-6fef-40be-b95e-9f9080ff8938@nvidia.com>
Date: Mon, 20 Oct 2025 16:45:38 -0400
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>,
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 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 10/20/2025 4:42 PM, John Hubbard wrote:
> 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.
> 

Sure, I will change to this wording for next posting. Thanks,

 - Joel