Re: [PATCH v8 4/9] of/iommu: Support dma-can-stall property

[Robin Murphy <robin.murphy@arm.com>]

On 2020-11-12 12:55, Jean-Philippe Brucker wrote:
> Copy the dma-can-stall property into the fwspec structure.

Can't we just handle this as a regular device property? It's not part of 
the actual IOMMU specifier, it doesn't need to be translated in any way, 
and AFAICS it's used a grand total of once, in a slow path. Simply 
treating it as the per-device property that it is should require zero 
additional code for DT, and a simple device_add_properties() call for IORT.

TBH that appears to be true of pasid-num-bits as well.

Robin.

> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
>   include/linux/iommu.h    | 2 ++
>   drivers/iommu/of_iommu.c | 5 ++++-
>   2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index a1c78c4cdeb1..9076fb592c8f 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -572,6 +572,7 @@ struct iommu_group *fsl_mc_device_group(struct device *dev);
>    * @iommu_fwnode: firmware handle for this device's IOMMU
>    * @iommu_priv: IOMMU driver private data for this device
>    * @num_pasid_bits: number of PASID bits supported by this device
> + * @can_stall: the device is allowed to stall
>    * @num_ids: number of associated device IDs
>    * @ids: IDs which this device may present to the IOMMU
>    */
> @@ -579,6 +580,7 @@ struct iommu_fwspec {
>   	const struct iommu_ops	*ops;
>   	struct fwnode_handle	*iommu_fwnode;
>   	u32			num_pasid_bits;
> +	bool			can_stall;
>   	unsigned int		num_ids;
>   	u32			ids[];
>   };
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index e505b9130a1c..d6255ca823d8 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -212,9 +212,12 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
>   		err = of_iommu_configure_device(master_np, dev, id);
>   
>   		fwspec = dev_iommu_fwspec_get(dev);
> -		if (!err && fwspec)
> +		if (!err && fwspec) {
>   			of_property_read_u32(master_np, "pasid-num-bits",
>   					     &fwspec->num_pasid_bits);
> +			fwspec->can_stall = of_property_read_bool(master_np,
> +								  "dma-can-stall");
> +		}
>   	}
>   
>   	/*
>