Re: [PATCH 08/10] iommu/tegra: Use tegra_dev_iommu_get_stream_id() in the remaining places

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

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On Tue, Nov 28, 2023 at 08:48:04PM -0400, Jason Gunthorpe wrote:
> This API was defined to formalize the access to internal iommu details on
> some Tegra SOCs, but a few callers got missed. Add them.
> 
> The helper already masks by 0xFFFF so remove this code from the callers.
> 
> Suggested-by: Thierry Reding <thierry.reding@gmail.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  drivers/dma/tegra186-gpc-dma.c                  |  8 +++-----
>  drivers/gpu/drm/nouveau/nvkm/subdev/ltc/gp10b.c |  7 ++-----
>  drivers/memory/tegra/tegra186.c                 | 12 ++++++------
>  3 files changed, 11 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-dma.c
> index fa4d4142a68a21..88547a23825b18 100644
> --- a/drivers/dma/tegra186-gpc-dma.c
> +++ b/drivers/dma/tegra186-gpc-dma.c
> @@ -1348,8 +1348,8 @@ static int tegra_dma_program_sid(struct tegra_dma_channel *tdc, int stream_id)
>  static int tegra_dma_probe(struct platform_device *pdev)
>  {
>  	const struct tegra_dma_chip_data *cdata = NULL;
> -	struct iommu_fwspec *iommu_spec;
> -	unsigned int stream_id, i;
> +	unsigned int i;
> +	u32 stream_id;
>  	struct tegra_dma *tdma;
>  	int ret;
>  
> @@ -1378,12 +1378,10 @@ static int tegra_dma_probe(struct platform_device *pdev)
>  
>  	tdma->dma_dev.dev = &pdev->dev;
>  
> -	iommu_spec = dev_iommu_fwspec_get(&pdev->dev);
> -	if (!iommu_spec) {
> +	if (!tegra_dev_iommu_get_stream_id(&pdev->dev, &stream_id)) {
>  		dev_err(&pdev->dev, "Missing iommu stream-id\n");
>  		return -EINVAL;
>  	}
> -	stream_id = iommu_spec->ids[0] & 0xffff;
>  
>  	ret = device_property_read_u32(&pdev->dev, "dma-channel-mask",
>  				       &tdma->chan_mask);
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/ltc/gp10b.c b/drivers/gpu/drm/nouveau/nvkm/subdev/ltc/gp10b.c
> index e7e8fdf3adab7a..b40fd1dbb21617 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/ltc/gp10b.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/ltc/gp10b.c
> @@ -28,16 +28,13 @@ static void
>  gp10b_ltc_init(struct nvkm_ltc *ltc)
>  {
>  	struct nvkm_device *device = ltc->subdev.device;
> -	struct iommu_fwspec *spec;
> +	u32 sid;
>  
>  	nvkm_wr32(device, 0x17e27c, ltc->ltc_nr);
>  	nvkm_wr32(device, 0x17e000, ltc->ltc_nr);
>  	nvkm_wr32(device, 0x100800, ltc->ltc_nr);
>  
> -	spec = dev_iommu_fwspec_get(device->dev);
> -	if (spec) {
> -		u32 sid = spec->ids[0] & 0xffff;
> -
> +	if (tegra_dev_iommu_get_stream_id(device->dev, &sid)) {
>  		/* stream ID */
>  		nvkm_wr32(device, 0x160000, sid << 2);

We could probably also remove the comment now since the function and
variable names make it obvious what's being written here.

>  	}
> diff --git a/drivers/memory/tegra/tegra186.c b/drivers/memory/tegra/tegra186.c
> index 533f85a4b2bdb7..3e4fbe94dd666e 100644
> --- a/drivers/memory/tegra/tegra186.c
> +++ b/drivers/memory/tegra/tegra186.c
> @@ -111,21 +111,21 @@ static void tegra186_mc_client_sid_override(struct tegra_mc *mc,
>  static int tegra186_mc_probe_device(struct tegra_mc *mc, struct device *dev)
>  {
>  #if IS_ENABLED(CONFIG_IOMMU_API)
> -	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
>  	struct of_phandle_args args;
>  	unsigned int i, index = 0;
> +	u32 sid;
>  
> +	WARN_ON(!tegra_dev_iommu_get_stream_id(dev, &sid));

I know the code previously didn't check for any errors, but we may want
to do so now. If tegra_dev_iommu_get_stream_id() ever fails we may end
up writing some undefined value into the override register.

I'm also unsure if WARN_ON() is appropriate here. I vaguely recall that
->probe_device() was called for all devices on the bus and not all of
them may have been associated with the IOMMU. Not all of them may in
fact access memory in the first place.

Perhaps I'm misremembering and the IOMMU core now takes care of only
calling this when fwspec is indeed valid?

Thierry

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