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

[Dmitry Osipenko <digetx@gmail.com>]

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?

>  drivers/gpu/drm/tegra/drm.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
> index 4a696fa274a3..0540b0741df6 100644
> --- a/drivers/gpu/drm/tegra/drm.c
> +++ b/drivers/gpu/drm/tegra/drm.c
> @@ -115,6 +115,10 @@ static int tegra_drm_load(struct drm_device *drm, unsigned long flags)
>  			goto free;
>  		}
>  
> +		err = iova_cache_get();
> +		if (err < 0)
> +			goto domain;
> +

Host1x also uses the alloc_iova(), though this allocation is actually invoked by
the DRM driver on requesting a channel. It is fine right now because DRM driver
is the only host1x user, but what about to add iova_cache_get() to the host1x
driver as well for consistency?

>  		geometry = &tegra->domain->geometry;
>  		gem_start = geometry->aperture_start;
>  		gem_end = geometry->aperture_end - CARVEOUT_SZ;
> @@ -205,11 +209,12 @@ static int tegra_drm_load(struct drm_device *drm, unsigned long flags)
>  	tegra_drm_fb_free(drm);
>  config:
>  	drm_mode_config_cleanup(drm);
> -
> +domain:
>  	if (tegra->domain) {
>  		mutex_destroy(&tegra->mm_lock);
>  		drm_mm_takedown(&tegra->mm);
>  		put_iova_domain(&tegra->carveout.domain);
> +		iova_cache_put();
>  		iommu_domain_free(tegra->domain);
>  	}
>  free:
> @@ -236,6 +241,7 @@ static void tegra_drm_unload(struct drm_device *drm)
>  		mutex_destroy(&tegra->mm_lock);
>  		drm_mm_takedown(&tegra->mm);
>  		put_iova_domain(&tegra->carveout.domain);
> +		iova_cache_put();
>  		iommu_domain_free(tegra->domain);
>  	}
>  
> 

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