linux-kernel - Re: [PATCH V7 2/4] iommu/arm-smmu-v3: Add device-tree support for CMDQV driver

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Message-ID: <1a224921-1e67-4699-a91d-89930db6147f@nvidia.com>
Date: Fri, 9 Jan 2026 09:45:02 +0000
From: Jon Hunter <jonathanh@...dia.com>
To: Ashish Mhetre <amhetre@...dia.com>, Nicolin Chen <nicolinc@...dia.com>
Cc: will@...nel.org, robin.murphy@....com, joro@...tes.org, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, thierry.reding@...il.com,
 vdumpa@...dia.com, jgg@...pe.ca, linux-arm-kernel@...ts.infradead.org,
 iommu@...ts.linux.dev, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH V7 2/4] iommu/arm-smmu-v3: Add device-tree support for
 CMDQV driver


On 07/01/2026 06:44, Ashish Mhetre wrote:
> 
> 
> On 12/20/2025 12:19 AM, Nicolin Chen wrote:
>> On Fri, Dec 19, 2025 at 10:48:22AM +0000, Jon Hunter wrote:
>>> On 18/12/2025 18:57, Nicolin Chen wrote:
>>>> On Thu, Dec 18, 2025 at 08:48:32AM +0000, Jon Hunter wrote:
>>>>> On 18/12/2025 06:32, Ashish Mhetre wrote:
>>>>>> On 12/18/2025 2:13 AM, Jon Hunter wrote:
>>>>>>>> +    smmu->impl_dev = &pdev->dev;
>>>>>>>> +    smmu->options |= ARM_SMMU_OPT_TEGRA241_CMDQV;
>>>>>>>> +    dev_info(smmu->dev, "found companion CMDQV device: %s\n",
>>>>>>>> +         dev_name(smmu->impl_dev));
>>>>>>> This seems a bit noisy. dev_dbg?
>>>>>>>
>>>>>> This info print is similar to what is there in ACPI path as well.
>>>>>> It's only a single print per SMMU at boot time. Should I still change
>>>>>> it to dev_dbg?
>>>>> Yes, I would.
>>>> It's really not that bad IMHO, I am not against that though..
>>>>
>>>> If we have to change that, we'd need another patch changing the
>>>> one in the ACPI path as well to keep things aligned.
>>> Regardless of what is already present, does not mean we need add more 
>>> prints
>>> to just say everything is OK.
>> This is how it looks like for each instance probe():
>>
>> [    2.709269] arm-smmu-v3 arm-smmu-v3.10.auto: found companion CMDQV 
>> device: NVDA200C:00
>> [    2.709273] arm-smmu-v3 arm-smmu-v3.10.auto: option mask 0x10
>> [    2.709618] arm-smmu-v3 arm-smmu-v3.10.auto: ias 48-bit, oas 48-bit 
>> (features 0x001e1fbf)
>> [    2.716236] arm-smmu-v3 arm-smmu-v3.10.auto: allocated 524288 
>> entries for cmdq
>> [    2.719432] arm-smmu-v3 arm-smmu-v3.10.auto: allocated 524288 
>> entries for evtq
>> [    2.725898] arm-smmu-v3 arm-smmu-v3.10.auto: allocated 524288 
>> entries for priq
>> [    2.736051] arm-smmu-v3 arm-smmu-v3.10.auto: allocated 524288 
>> entries for vcmdq0
>> [    2.742553] arm-smmu-v3 arm-smmu-v3.10.auto: allocated 524288 
>> entries for vcmdq1
>> [    2.742586] arm-smmu-v3 arm-smmu-v3.10.auto: msi_domain absent - 
>> falling back to wired irqs
>> [    2.742759] arm-smmu-v3 arm-smmu-v3.10.auto: no priq irq - PRI will 
>> be broken
>>
>> On a second thought: The CMDQV device has a very unclear naming in
>> ACPI path: "NVDA200C:00". So, printing it gives us a hint for any
>> later warning/error tagged with "NVDA200C:00".
>>
>> Now, for DT, it might be okay to not print it. But making the two
>> paths asymmetric feels odd. So, is it really worth nitpicking here
>> given that each SMMU already prints quite a few lines on probe()?
>>
>> Nicolin
> 
> Hi Jon, Nic,
> 
> Shall I keep this print or send a new version removing it?

Make it dev_dbg() and you can always enable it if you want it. 99.9% of 
the time you will not need this.

Thanks!
Jon

-- 
nvpublic