linux-kernel - Re: [PATCH] iommu/tegra-smmu: Fix mc errors on tegra124-nyan

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Date:   Thu, 11 Mar 2021 15:06:25 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     joro@...tes.org, thierry.reding@...il.com, will@...nel.org,
        guillaume.tucker@...labora.com, vdumpa@...dia.com,
        jonathanh@...dia.com, linux-tegra@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/tegra-smmu: Fix mc errors on tegra124-nyan

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