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

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Date:   Tue, 2 Mar 2021 15:08:59 -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 Sat, Feb 27, 2021 at 12:59:17PM +0300, Dmitry Osipenko wrote:
> 25.02.2021 09:27, Nicolin Chen пишет:
> ...
> >> The partially revert should be okay, but it's not clear to me what makes
> >> difference for T124 since I don't see that problem on T30, which also
> >> has active display at a boot time.
> > 
> > Hmm..do you see ->attach_dev() is called from host1x_client_iommu_attach
> > or from of_dma_configure_id/arch_setup_dma_ops?
> > 
> 
> I applied yours debug-patch, please see dmesg.txt attached to the email.
> Seems probe-defer of the tegra-dc driver prevents the implicit
> tegra_smmu_attach_dev, so it happens to work by accident.

> [    0.327826] tegra-dc 54200000.dc: -------tegra_smmu_of_xlate: id 1
> [    0.328641] [<c052ec75>] (tegra_smmu_of_xlate) from [<c052e591>] (of_iommu_xlate+0x51/0x70)
> [    0.328740] [<c052e591>] (of_iommu_xlate) from [<c052e6d7>] (of_iommu_configure+0x127/0x150)
> [    0.328896] [<c052e6d7>] (of_iommu_configure) from [<c073f697>] (of_dma_configure_id+0x1fb/0x2ec)
> [    0.329060] [<c073f697>] (of_dma_configure_id) from [<c059743f>] (really_probe+0x7b/0x2a0)
> [    0.331438] tegra-dc 54200000.dc: --------tegra_smmu_probe_device, 822
> [    0.332234] [<c052ebed>] (tegra_smmu_probe_device) from [<c052bd6d>] (__iommu_probe_device+0x35/0x1c4)
> [    0.332391] [<c052bd6d>] (__iommu_probe_device) from [<c052c3cd>] (iommu_probe_device+0x19/0xec)
> [    0.332545] [<c052c3cd>] (iommu_probe_device) from [<c052e6ab>] (of_iommu_configure+0xfb/0x150)
> [    0.332701] [<c052e6ab>] (of_iommu_configure) from [<c073f697>] (of_dma_configure_id+0x1fb/0x2ec)
> [    0.332804] [<c073f697>] (of_dma_configure_id) from [<c059743f>] (really_probe+0x7b/0x2a0)
> [    0.335202] tegra-dc 54200000.dc: ---------iommu_group_get_for_dev, 1572
> [    0.335292] tegra-dc 54200000.dc: ---------tegra_smmu_device_group, 862
> [    0.335474] tegra-dc 54200000.dc: ---------tegra_smmu_device_group, 909: 1: drm
> [    0.335566] tegra-dc 54200000.dc: ---------iommu_group_get_for_dev, 1574
> [    0.335718] tegra-dc 54200000.dc: ---------iommu_group_add_device, 858
> [    0.335862] tegra-dc 54200000.dc: Adding to iommu group 1
> [    0.335955] tegra-dc 54200000.dc: ---------iommu_alloc_default_domain, 1543: type 3
> [    0.336101] iommu: ------iommu_group_alloc_default_domain: platform, (null), drm
> [    0.336187] ---------tegra_smmu_domain_alloc, 284: type 3
 [    0.336968] [<c0a0ff45>] (tegra_smmu_domain_alloc) from [<c0a0f87b>] (iommu_group_alloc_default_domain+0x4b/0xfa)
> [    0.337127] [<c0a0f87b>] (iommu_group_alloc_default_domain) from [<c052c41d>] (iommu_probe_device+0x69/0xec)
> [    0.337285] [<c052c41d>] (iommu_probe_device) from [<c052e6ab>] (of_iommu_configure+0xfb/0x150)
> [    0.337441] [<c052e6ab>] (of_iommu_configure) from [<c073f697>] (of_dma_configure_id+0x1fb/0x2ec)
> [    0.337599] [<c073f697>] (of_dma_configure_id) from [<c059743f>] (really_probe+0x7b/0x2a0)
> [    0.339913] tegra-dc 54200000.dc: ---------iommu_probe_device, 272
> [    0.348144] tegra-dc 54200000.dc: failed to probe RGB output: -517

Hmm..not sure where this EPROBE_DEFER comes from. But you are right,
as of_dma_configure_id() returns because of that so it didn't run to
arch_setup_dma_ops() call, which allocates an UNMANAGED iommu domain
and attaches DC to it on Tegra124.

By the way, anyone can accept this change? It doesn't feel right to
leave a regression in the newer release...