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

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Message-ID: <20210310221707.GB10431@Asurada-Nvidia>
Date:   Wed, 10 Mar 2021 14:17:07 -0800
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Dmitry Osipenko <digetx@...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

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?