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Date:   Tue, 18 Oct 2022 07:13:43 +0100
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Subject: Re: [PATCH v4 05/16] iommu: Move bus setup to IOMMU device
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Content-Language: en-US
To:     Robin Murphy <robin.murphy@arm.com>, joro@8bytes.org,
        Thierry Reding <treding@nvidia.com>,
        Dmitry Osipenko <digetx@gmail.com>
Cc:     will@kernel.org, iommu@lists.linux.dev,
        linux-arm-kernel@lists.infradead.org, baolu.lu@linux.intel.com,
        kevin.tian@intel.com, suravee.suthikulpanit@amd.com,
        vasant.hegde@amd.com, mjrosato@linux.ibm.com,
        schnelle@linux.ibm.com, linux-kernel@vger.kernel.org,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>
References: <cover.1660572783.git.robin.murphy@arm.com>
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 <583c4689-844d-2ae2-79fb-4750b21c4304@arm.com>
From:   Jon Hunter <jonathanh@nvidia.com>
In-Reply-To: <583c4689-844d-2ae2-79fb-4750b21c4304@arm.com>
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On 06/10/2022 16:27, Robin Murphy wrote:
> On 2022-10-06 15:01, Jon Hunter wrote:
>> Hi Robin,
>>
>> On 15/08/2022 17:20, Robin Murphy wrote:
>>> Move the bus setup to iommu_device_register(). This should allow
>>> bus_iommu_probe() to be correctly replayed for multiple IOMMU instances,
>>> and leaves bus_set_iommu() as a glorified no-op to be cleaned up next.
>>>
>>> At this point we can also handle cleanup better than just rolling back
>>> the most-recently-touched bus upon failure - which may release devices
>>> owned by other already-registered instances, and still leave devices on
>>> other buses with dangling pointers to the failed instance. Now it's easy
>>> to clean up the exact footprint of a given instance, no more, no less.
>>
>>
>> Since this change, I have noticed that the DRM driver on Tegra20 is 
>> failing to probe and I am seeing ...
>>
>>   tegra-gr2d 54140000.gr2d: failed to attach to domain: -19
>>   drm drm: failed to initialize 54140000.gr2d: -19
>>
>> Bisect points to this change and reverting it fixes it. Let me know if 
>> you have any thoughts.
> 
> Oh, apparently what's happened is that I've inadvertently enabled the 
> tegra-gart driver, since it seems that *wasn't* calling bus_set_iommu() 
> before. Looking at the history, it appears to have been that way since 
> c7e3ca515e78 ("iommu/tegra: gart: Do not register with bus"), so 
> essentially that driver has been broken and useless for close to 8 years 
> now :(
> 
> Given that, I'd be inclined to "fix" it as below, or just give up and 
> delete the whole thing.
> 
> Thanks,
> Robin.
> 
> ----->8-----
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 5c5cb5bee8b6..7b3f7fd6e527 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -230,6 +230,7 @@ config TEGRA_IOMMU_GART
>       bool "Tegra GART IOMMU Support"
>       depends on ARCH_TEGRA_2x_SOC
>       depends on TEGRA_MC
> +    depends on BROKEN
>       select IOMMU_API
>       help
>         Enables support for remapping discontiguous physical memory


Thanks Robin. This works for me.

Thierry, Dmitry, we need a fix for v6.1 and so OK with the above?

Jon

-- 
nvpublic