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

From: Robin Murphy
Date: Thu Oct 06 2022 - 11:27:56 EST

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.


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
Enables support for remapping discontiguous physical memory