linux-kernel - Re: [PATCH v4 05/16] iommu: Move bus setup to IOMMU device registration

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Message-ID: <41293685-54aa-6fa3-ca41-189fdbb7e8b0@nvidia.com>
Date:   Tue, 18 Oct 2022 07:13:43 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Robin Murphy <robin.murphy@....com>, joro@...tes.org,
        Thierry Reding <treding@...dia.com>,
        Dmitry Osipenko <digetx@...il.com>
Cc:     will@...nel.org, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, baolu.lu@...ux.intel.com,
        kevin.tian@...el.com, suravee.suthikulpanit@....com,
        vasant.hegde@....com, mjrosato@...ux.ibm.com,
        schnelle@...ux.ibm.com, linux-kernel@...r.kernel.org,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v4 05/16] iommu: Move bus setup to IOMMU device
 registration


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