[PATCH v2] gpu: host1x: Avoid trying to use GART on Tegra20

[Jon Hunter]

On 20/10/2022 15:23, Robin Murphy wrote:
> Since commit c7e3ca515e78 ("iommu/tegra: gart: Do not register with
> bus") quite some time ago, the GART driver has effectively disabled
> itself to avoid issues with the GPU driver expecting it to work in ways
> that it doesn't. As of commit 57365a04c921 ("iommu: Move bus setup to
> IOMMU device registration") that bodge no longer works, but really the
> GPU driver should be responsible for its own behaviour anyway. Make the
> workaround explicit.
> 
> Reported-by: Jon Hunter <jonathanh at nvidia.com>
> Suggested-by: Dmitry Osipenko <digetx at gmail.com>
> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
> ---
> 
> v2: Cover DRM instance too, move into *_wants_iommu() for consistency
> 
>   drivers/gpu/drm/tegra/drm.c | 4 ++++
>   drivers/gpu/host1x/dev.c    | 4 ++++
>   2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
> index 6748ec1e0005..a1f909dac89a 100644
> --- a/drivers/gpu/drm/tegra/drm.c
> +++ b/drivers/gpu/drm/tegra/drm.c
> @@ -1093,6 +1093,10 @@ static bool host1x_drm_wants_iommu(struct host1x_device *dev)
>   	struct host1x *host1x = dev_get_drvdata(dev->dev.parent);
>   	struct iommu_domain *domain;
>   
> +	/* Our IOMMU usage policy doesn't currently play well with GART */
> +	if (of_machine_is_compatible("nvidia,tegra20"))
> +		return false;
> +
>   	/*
>   	 * If the Tegra DRM clients are backed by an IOMMU, push buffers are
>   	 * likely to be allocated beyond the 32-bit boundary if sufficient
> diff --git a/drivers/gpu/host1x/dev.c b/drivers/gpu/host1x/dev.c
> index 0cd3f97e7e49..f60ea24db0ec 100644
> --- a/drivers/gpu/host1x/dev.c
> +++ b/drivers/gpu/host1x/dev.c
> @@ -292,6 +292,10 @@ static void host1x_setup_virtualization_tables(struct host1x *host)
>   
>   static bool host1x_wants_iommu(struct host1x *host1x)
>   {
> +	/* Our IOMMU usage policy doesn't currently play well with GART */
> +	if (of_machine_is_compatible("nvidia,tegra20"))
> +		return false;
> +
>   	/*
>   	 * If we support addressing a maximum of 32 bits of physical memory
>   	 * and if the host1x firewall is enabled, there's no need to enable


Thanks! Works for me.

Tested-by: Jon Hunter <jonathanh at nvidia.com>

Cheers
Jon

-- 
nvpublic