On 23.04.2018 09:57, Thierry Reding wrote:
> From: Thierry Reding <tred...@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 <tred...@nvidia.com>
> ---
>  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;
> +
>               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();

I've spotted that this ^ is incorrect. This will put the iova_cache without
getting it if iova_cache_get() failed.

>               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);
>       }
>  
> 

Thierry, please update the patch:

diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index 4a59ac4d7793..26ce98479fb6 100644
--- a/drivers/gpu/drm/tegra/drm.c
+++ b/drivers/gpu/drm/tegra/drm.c
@@ -98,6 +98,10 @@ static int tegra_drm_load(struct drm_device *drm, unsigned
long flags)
                        goto free;
                }

+               err = iova_cache_get();
+               if (err < 0)
+                       goto domain;
+
                geometry = &tegra->domain->geometry;
                gem_start = geometry->aperture_start;
                gem_end = geometry->aperture_end - CARVEOUT_SZ;
@@ -194,8 +198,11 @@ static int tegra_drm_load(struct drm_device *drm, unsigned
long flags)
                mutex_destroy(&tegra->mm_lock);
                drm_mm_takedown(&tegra->mm);
                put_iova_domain(&tegra->carveout.domain);
-               iommu_domain_free(tegra->domain);
+               iova_cache_put();
        }
+domain:
+       if (tegra->domain)
+               iommu_domain_free(tegra->domain);
 free:
        kfree(tegra);
        return err;
@@ -220,6 +227,7 @@ 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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