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

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Date:   Sun, 28 Mar 2021 18:25:52 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>, thierry.reding@...il.com
Cc:     joro@...tes.org, 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

03.03.2021 12:47, Dmitry Osipenko пишет:
> 03.03.2021 02:08, Nicolin Chen пишет:
>> 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.
> DC driver on Nexus 7 depends on LVDS bridge and display panel, which
> cause the probe defer.
> 
>> 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...

Guys, I have a good and bad news.

The good news is that I figured out why I didn't see this problem on
Nexus 7 and the reason is that I had CONFIG_ARM_DMA_USE_IOMMU=n.

The other good news is that I have a simple workaround which fixes the
implicit IOMMU problem by deferring the ASID enabling for display clients.

The bad news is that CONFIG_ARM_DMA_USE_IOMMU=y breaks GPU (DRM, host1x)
drivers because they aren't properly prepared to this case and
CONFIG_ARM_DMA_USE_IOMMU is enabled in multi-platform kernel config. I
will try to fix up the drivers, but not sure how much time this may take.