linux-kernel - Re: [PATCH 0/3] NVIDIA Tegra210 NVJPG support

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Message-ID: <ccf6ab71-bdf2-4e3d-a8e5-228c24bcf3bb@kapsi.fi>
Date: Tue, 17 Jun 2025 13:34:18 +0900
From: Mikko Perttunen <cyndis@...si.fi>
To: Diogo Ivo <diogo.ivo@...nico.ulisboa.pt>,
 Thierry Reding <thierry.reding@...il.com>
Cc: Mikko Perttunen <mperttunen@...dia.com>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Jonathan Hunter <jonathanh@...dia.com>,
 Philipp Zabel <p.zabel@...gutronix.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
 devicetree@...r.kernel.org
Subject: Re: [PATCH 0/3] NVIDIA Tegra210 NVJPG support

On 6/16/25 7:23 PM, Diogo Ivo wrote:
> 
> 
> On 6/12/25 2:55 AM, Mikko Perttunen wrote:
>> On 6/12/25 12:06 AM, Thierry Reding wrote:
>>> On Wed, Jun 11, 2025 at 01:05:40PM +0100, Diogo Ivo wrote:
>>>> I have a question here, what exactly are the stream IDs? While working
>>>> on the driver this came up and I didn't manage to figure it out.
>>>
>>> Stream IDs are a way to identify memory transactions as belonging to a
>>> certain device. This comes into play when working with the IOMMU (which
>>> is a Tegra SMMU on Tegra210 and earlier, and an ARM SMMU on Tegra) and
>>> is used to isolate DMA capable devices. Basically for every stream ID
>>> you get a separate I/O address space. NVJPG will have its own address
>>> space, and so will VIC. Each device can only access whatever has been
>>> mapped to it's I/O address space. That means NVJPG can't interfere with
>>> VIC and vice-versa. And neither can any of these engines read from or
>>> write to random system memory if badly programmed.
>>>
>>> For Tegra SMMU there's no such thing as programmable stream IDs, so the
>>> stream ID is fixed for the given device.
>>>
>>> On newer chips (Tegra186 and later, or maybe it wasn't until Tegra194),
>>
>> Tegra186 and newer -- all chips with the ARM SMMU. To add a little 
>> bit, each engine can address two stream IDs, one for firmware and one 
>> for data. All user specified buffers are mapped into the data IOMMU 
>> domain, and these are switched between jobs / applications.
>>
>> As an aside, currently each engine has its own firmware stream ID, but 
>> that's a bit wasteful, since the kernel allocates a separate IOMMU 
>> domain for each. The firmwares are all read-only so they could be in a 
>> shared one. We've had to consolidate these on some platforms that ran 
>> out of IOMMU domains otherwise. Not really a concern with upstream 
>> platforms, though.
> 
> Does this dual Stream ID also apply to Tegra210?

No, only Tegra186 and later (chips with ARM SMMU).

> 
>> Also need to program the THI_STREAMID / TRANSCFG registers during boot.
> 
> Thanks,
> Diogo
>