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Subject: Re: [PATCH] iommu/tegra-smmu: Fix mc errors on tegra124-nyan
To:     Nicolin Chen <nicoleotsuka@gmail.com>
Cc:     joro@8bytes.org, thierry.reding@gmail.com, will@kernel.org,
        guillaume.tucker@collabora.com, vdumpa@nvidia.com,
        jonathanh@nvidia.com, linux-tegra@vger.kernel.org,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
References: <20210218220702.1962-1-nicoleotsuka@gmail.com>
 <a8a7a0af-895f-9d79-410d-5dd03ebbd6dd@gmail.com>
 <7714f272-3862-84ac-306d-86363a1c4880@gmail.com>
 <20210310221707.GB10431@Asurada-Nvidia>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <8c2f5d94-8835-9994-21aa-660df29d383c@gmail.com>
Date:   Thu, 11 Mar 2021 15:06:25 +0300
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11.03.2021 01:17, Nicolin Chen пишет:
> On Wed, Mar 10, 2021 at 11:22:57PM +0300, Dmitry Osipenko wrote:
>> 10.03.2021 22:13, Dmitry Osipenko пишет:
>>> I found that this patch introduced a serious regression on Tegra30 using
>>> today's linux-next. Tegra30 has two 3d h/w blocks connected in SLI and
>>> only one of the blocks is now attached to IOMMU domain, meaning that GPU
>>> is unusable now. All 3d, 2d and display devices share the same "DRM"
>>> group on Tegra30.
>>>
>>> Nicolin, please let me know if have any suggestions. I may take a closer
>>> look a day later, for now I'll just revert this patch locally. Thanks in
>>> advance.
>>>
>>
>> Actually, this was easy to fix:
>>
>> diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
>> index 97eb62f667d2..639d5ceab60b 100644
>> --- a/drivers/iommu/tegra-smmu.c
>> +++ b/drivers/iommu/tegra-smmu.c
>> @@ -853,8 +853,6 @@ static struct iommu_device
>> *tegra_smmu_probe_device(struct device *dev)
>>
>>  			if (err < 0)
>>  				return ERR_PTR(err);
>> -
>> -			break;
> 
> Hmm..I don't understand why this "break" causes problems on Tegra30.
> The older versions that used _find()+configure() had it also, e.g.:
> https://elixir.bootlin.com/linux/v5.9.16/source/drivers/iommu/tegra-smmu.c#L760
> 
> Dmitry, do you have any idea?
> 

The older variant of tegra_smmu_attach_dev() didn't use fwspec [1], that
makes the difference. In other words, the older variant of
tegra_smmu_probe_device() was already buggy, but the bug was masked by
the tegra_smmu_attach_dev() that didn't use the fwspec.

[1]
https://elixir.bootlin.com/linux/v5.10.22/source/drivers/iommu/tegra-smmu.c#L476