Subject: Re: [RFC PATCH v3 6/6] of: Add plumbing for restricted DMA pool

From: Florian Fainelli <[email-masked]>
Date: Tue, 12 Jan 2021 15:48:24 -0800

On 1/5/21 7:41 PM, 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 <[email-masked]>
> ---

[snip]

> +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));

You could have an early check for count < 0, along with an error
message, if that is deemed useful.

> +	for (i = 0; i < count; i++) {
> +		node = of_parse_phandle(dev->of_node, "memory-region", i);
> +		if (of_device_is_compatible(node, "restricted-dma-pool"))

And you may want to add here an of_device_is_available(node). A platform
that provides the Device Tree firmware and try to support multiple
different SoCs may try to determine if an IOMMU is present, and if it
is, it could be marking the restriced-dma-pool region with a 'status =
"disabled"' property, or any variant of that scheme.

> +			return of_reserved_mem_device_init_by_idx(
> +				dev, dev->of_node, i);

This does not seem to be supporting more than one memory region, did not
you want something like instead:

		ret = of_reserved_mem_device_init_by_idx(...);
		if (ret)
			return ret;

> +	}
> +
> +	return 0;
> +}
> diff --git a/drivers/of/device.c b/drivers/of/device.c
> index aedfaaafd3e7..e2c7409956ab 100644
> --- a/drivers/of/device.c
> +++ b/drivers/of/device.c
> @@ -182,6 +182,10 @@ int of_dma_configure_id(struct device *dev, struct device_node *np,
>  	arch_setup_dma_ops(dev, dma_start, size, iommu, coherent);
>  
>  	dev->dma_range_map = map;
> +
> +	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 d9e6a324de0a..28a2dfa197ba 100644
> --- a/drivers/of/of_private.h
> +++ b/drivers/of/of_private.h
> @@ -161,12 +161,17 @@ 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 */
> 

-- 
Florian