Re: [PATCH 2/2] drm/tegra: Acquire a reference to the IOVA cache

[Thierry Reding <thierry.reding@gmail.com>]

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On Mon, Apr 23, 2018 at 11:43:16AM +0300, Dmitry Osipenko wrote:
> On 23.04.2018 11:41, Dmitry Osipenko wrote:
> > On 23.04.2018 11:34, Dmitry Osipenko wrote:
> >> On 23.04.2018 09:57, Thierry Reding wrote:
> >>> From: Thierry Reding <treding@nvidia.com>
> >>>
> >>> The IOVA API uses a memory cache to allocate IOVA nodes from. To make
> >>> sure that this cache is available, obtain a reference to it and release
> >>> the reference when the cache is no longer needed.
> >>>
> >>> On 64-bit ARM this is hidden by the fact that the DMA mapping API gets
> >>> that reference and never releases it. On 32-bit ARM, however, the DMA
> >>> mapping API doesn't do that, so allocation of IOVA nodes fails.
> >>>
> >>> Signed-off-by: Thierry Reding <treding@nvidia.com>
> >>> ---
> >>
> >> Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
> >> Tested-by: Dmitry Osipenko <digetx@gmail.com>
> >>
> >> CONFIG_TEGRA_IOMMU_SMMU is enabled in the default kernel configs and hence DRM
> >> should fail to probe on t124 since 4.11. What about to add stable tag for v4.11+
> >> here to unbreak stable kernels as well?
> > 
> > IOMMU node for host1x was added to t124 DT in kernel v4.14, so s/4.11/4.14/.
> 
> On the other hand nothing stops to use newer DT with older kernel.

I've applied this and added:

	Fixes: ad92601521ea ("drm/tegra: Add Tegra DRM allocation API")

Since that's the commit that introduced the iova API usage. It seems
like we also need a fix in drivers/gpu/host1x to grab a reference to
this IOVA cache because the host1x driver also makes use of that. It
looks as if this patch currently papers over that bug, and there's
very little chance that anyone will use the host1x driver without the
Tegra DRM driver. However, it's probably best to still fix it to avoid
future exposure.

I'll go type that patch up now.

Thierry

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