Re: [PATCH v5 16/16] of: Add plumbing for restricted DMA pool

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

On 2021-04-22 09:15, Claire Chang wrote:
> If a device is not behind an IOMMU, we look up the device node and set
> up the restricted DMA when the restricted-dma-pool is presented.
> 
> Signed-off-by: Claire Chang <tientzu@chromium.org>
> ---
>   drivers/of/address.c    | 25 +++++++++++++++++++++++++
>   drivers/of/device.c     |  3 +++
>   drivers/of/of_private.h |  5 +++++
>   3 files changed, 33 insertions(+)
> 
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index 54f221dde267..fff3adfe4986 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -8,6 +8,7 @@
>   #include <linux/logic_pio.h>
>   #include <linux/module.h>
>   #include <linux/of_address.h>
> +#include <linux/of_reserved_mem.h>
>   #include <linux/pci.h>
>   #include <linux/pci_regs.h>
>   #include <linux/sizes.h>
> @@ -1109,6 +1110,30 @@ bool of_dma_is_coherent(struct device_node *np)
>   }
>   EXPORT_SYMBOL_GPL(of_dma_is_coherent);
>   
> +int of_dma_set_restricted_buffer(struct device *dev)
> +{
> +	struct device_node *node;
> +	int count, i;
> +
> +	if (!dev->of_node)
> +		return 0;
> +
> +	count = of_property_count_elems_of_size(dev->of_node, "memory-region",
> +						sizeof(phandle));
> +	for (i = 0; i < count; i++) {
> +		node = of_parse_phandle(dev->of_node, "memory-region", i);
> +		/* There might be multiple memory regions, but only one
> +		 * restriced-dma-pool region is allowed.
> +		 */

What's the use-case for having multiple regions if the restricted pool 
is by definition the only one accessible?

Robin.

> +		if (of_device_is_compatible(node, "restricted-dma-pool") &&
> +		    of_device_is_available(node))
> +			return of_reserved_mem_device_init_by_idx(
> +				dev, dev->of_node, i);
> +	}
> +
> +	return 0;
> +}
> +
>   /**
>    * of_mmio_is_nonposted - Check if device uses non-posted MMIO
>    * @np:	device node
> diff --git a/drivers/of/device.c b/drivers/of/device.c
> index c5a9473a5fb1..d8d865223e51 100644
> --- a/drivers/of/device.c
> +++ b/drivers/of/device.c
> @@ -165,6 +165,9 @@ int of_dma_configure_id(struct device *dev, struct device_node *np,
>   
>   	arch_setup_dma_ops(dev, dma_start, size, iommu, coherent);
>   
> +	if (!iommu)
> +		return of_dma_set_restricted_buffer(dev);
> +
>   	return 0;
>   }
>   EXPORT_SYMBOL_GPL(of_dma_configure_id);
> diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
> index d717efbd637d..e9237f5eff48 100644
> --- a/drivers/of/of_private.h
> +++ b/drivers/of/of_private.h
> @@ -163,12 +163,17 @@ struct bus_dma_region;
>   #if defined(CONFIG_OF_ADDRESS) && defined(CONFIG_HAS_DMA)
>   int of_dma_get_range(struct device_node *np,
>   		const struct bus_dma_region **map);
> +int of_dma_set_restricted_buffer(struct device *dev);
>   #else
>   static inline int of_dma_get_range(struct device_node *np,
>   		const struct bus_dma_region **map)
>   {
>   	return -ENODEV;
>   }
> +static inline int of_dma_get_restricted_buffer(struct device *dev)
> +{
> +	return -ENODEV;
> +}
>   #endif
>   
>   #endif /* _LINUX_OF_PRIVATE_H */
>