[PATCH v2 09/25] iommu/fsl_pamu: Implement an IDENTITY domain

[Robin Murphy]

On 2023-05-16 01:00, Jason Gunthorpe wrote:
> Robin was able to check the documentation and what fsl_pamu has
> historically called detach_dev() is really putting the IOMMU into an
> IDENTITY mode.

Unfortunately it was the other way around - it's the call to 
fsl_setup_liodns() from fsl_pamu_probe() which leaves everything in 
bypass by default (the PAACE_ATM_NO_XLATE part, IIRC), whereas the 
detach_device() call here ends up disabling the given device's LIODN 
altogether. There doesn't appear to have ever been any code anywhere for 
putting things *back* into bypass after using a VFIO domain, so as-is 
these default domains would probably break all DMA :(

Thanks,
Robin.

> Move to the new core support for ARM_DMA_USE_IOMMU by defining
> ops->identity_domain. This is a ppc driver without any dma_ops, so ensure
> the identity translation is the default domain.
> 
> Signed-off-by: Jason Gunthorpe <jgg at nvidia.com>
> ---
>   drivers/iommu/fsl_pamu_domain.c | 32 +++++++++++++++++++++++++++++---
>   1 file changed, 29 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/fsl_pamu_domain.c b/drivers/iommu/fsl_pamu_domain.c
> index bce37229709965..ca4f5ebf028783 100644
> --- a/drivers/iommu/fsl_pamu_domain.c
> +++ b/drivers/iommu/fsl_pamu_domain.c
> @@ -283,15 +283,21 @@ static int fsl_pamu_attach_device(struct iommu_domain *domain,
>   	return ret;
>   }
>   
> -static void fsl_pamu_set_platform_dma(struct device *dev)
> +static int fsl_pamu_identity_attach(struct iommu_domain *platform_domain,
> +				    struct device *dev)
>   {
>   	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> -	struct fsl_dma_domain *dma_domain = to_fsl_dma_domain(domain);
> +	struct fsl_dma_domain *dma_domain;
>   	const u32 *prop;
>   	int len;
>   	struct pci_dev *pdev = NULL;
>   	struct pci_controller *pci_ctl;
>   
> +	if (domain == platform_domain || !domain)
> +		return 0;
> +
> +	dma_domain = to_fsl_dma_domain(domain);
> +
>   	/*
>   	 * Use LIODN of the PCI controller while detaching a
>   	 * PCI device.
> @@ -312,8 +318,18 @@ static void fsl_pamu_set_platform_dma(struct device *dev)
>   		detach_device(dev, dma_domain);
>   	else
>   		pr_debug("missing fsl,liodn property at %pOF\n", dev->of_node);
> +	return 0;
>   }
>   
> +static struct iommu_domain_ops fsl_pamu_identity_ops = {
> +	.attach_dev = fsl_pamu_identity_attach,
> +};
> +
> +static struct iommu_domain fsl_pamu_identity_domain = {
> +	.type = IOMMU_DOMAIN_IDENTITY,
> +	.ops = &fsl_pamu_identity_ops,
> +};
> +
>   /* Set the domain stash attribute */
>   int fsl_pamu_configure_l1_stash(struct iommu_domain *domain, u32 cpu)
>   {
> @@ -447,12 +463,22 @@ static struct iommu_device *fsl_pamu_probe_device(struct device *dev)
>   	return &pamu_iommu;
>   }
>   
> +static int fsl_pamu_def_domain_type(struct device *dev)
> +{
> +	/*
> +	 * This platform does not use dma_ops at all so the normally the iommu
> +	 * must be in identity mode
> +	 */
> +	return IOMMU_DOMAIN_IDENTITY;
> +}
> +
>   static const struct iommu_ops fsl_pamu_ops = {
> +	.identity_domain = &fsl_pamu_identity_domain,
> +	.def_domain_type = &fsl_pamu_def_domain_type,
>   	.capable	= fsl_pamu_capable,
>   	.domain_alloc	= fsl_pamu_domain_alloc,
>   	.probe_device	= fsl_pamu_probe_device,
>   	.device_group   = fsl_pamu_device_group,
> -	.set_platform_dma_ops = fsl_pamu_set_platform_dma,
>   	.default_domain_ops = &(const struct iommu_domain_ops) {
>   		.attach_dev	= fsl_pamu_attach_device,
>   		.iova_to_phys	= fsl_pamu_iova_to_phys,