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

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Message-ID: <583c4689-844d-2ae2-79fb-4750b21c4304@arm.com>
Date:   Thu, 6 Oct 2022 16:27:39 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Jon Hunter <jonathanh@...dia.com>, joro@...tes.org
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>,
        Thierry Reding <treding@...dia.com>
Subject: Re: [PATCH v4 05/16] iommu: Move bus setup to IOMMU device
 registration

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