Re: [PATCH v3 3/8] of/address: Introduce of_dma_get_max_cpu_address()

Rob Herring
2020-10-14T22:03:05Z

On Wed, Oct 14, 2020 at 2:12 PM Nicolas Saenz Julienne
<nsaenzjulienne@suse.de> wrote:
>
> Introduce of_dma_get_max_cpu_address(), which provides the highest CPU
> physical address addressable by all DMA masters in the system. It's
> specially useful for setting memory zones sizes at early boot time.
>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
>
> ---
>
> Changes since v2:
> - Use PHYS_ADDR_MAX
> - return phys_dma_t
> - Rename function
> - Correct subject
> - Add support to start parsing from an arbitrary device node in order
> for the function to work with unit tests
>
> drivers/of/address.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/of.h | 7 +++++++
> 2 files changed, 49 insertions(+)
>
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index eb9ab4f1e80b..b5a9695aaf82 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -1024,6 +1024,48 @@ int of_dma_get_range(struct device_node *np, const struct bus_dma_region **map)
> }
> #endif /* CONFIG_HAS_DMA */
>
> +/**
> + * of_dma_get_max_cpu_address - Gets highest CPU address suitable for DMA
> + * @np: The node to start searching from or NULL to start from the root
> + *
> + * Gets the highest CPU physical address that is addressable by all DMA masters
> + * in the system (or subtree when np is non-NULL). If no DMA constrained device
> + * is found, it returns PHYS_ADDR_MAX.
> + */
> +phys_addr_t __init of_dma_get_max_cpu_address(struct device_node *np)
> +{
> + phys_addr_t max_cpu_addr = PHYS_ADDR_MAX;

One issue with using phys_addr_t is it may be 32-bit even though the
DT is 64-bit addresses. LPAE capable system with LPAE disabled. Maybe
the truncation is fine here? Maybe not.

> + struct of_range_parser parser;
> + phys_addr_t subtree_max_addr;
> + struct device_node *child;
> + phys_addr_t cpu_end = 0;
> + struct of_range range;
> + const __be32 *ranges;
> + int len;
> +
> + if (!np)
> + np = of_root;
> +
> + ranges = of_get_property(np, "dma-ranges", &len);

I'm not really following why you changed the algorithm here. You're
skipping disabled nodes which is good. Was there some other reason?

> + if (ranges && len) {
> + of_dma_range_parser_init(&parser, np);
> + for_each_of_range(&parser, &range)
> + if (range.cpu_addr + range.size > cpu_end)
> + cpu_end = range.cpu_addr + range.size;
> +
> + if (max_cpu_addr > cpu_end)
> + max_cpu_addr = cpu_end;
> + }
> +
> + for_each_available_child_of_node(np, child) {
> + subtree_max_addr = of_dma_get_max_cpu_address(child);
> + if (max_cpu_addr > subtree_max_addr)
> + max_cpu_addr = subtree_max_addr;
> + }
> +
> + return max_cpu_addr;
> +}
> +
> /**
> * of_dma_is_coherent - Check if device is coherent
> * @np: device node
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 481ec0467285..db8db8f2c967 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -558,6 +558,8 @@ int of_map_id(struct device_node *np, u32 id,
> const char *map_name, const char *map_mask_name,
> struct device_node **target, u32 *id_out);
>
> +phys_addr_t of_dma_get_max_cpu_address(struct device_node *np);
> +
> #else /* CONFIG_OF */
>
> static inline void of_core_init(void)
> @@ -995,6 +997,11 @@ static inline int of_map_id(struct device_node *np, u32 id,
> return -EINVAL;
> }
>
> +static inline phys_addr_t of_dma_get_max_cpu_address(struct device_node *np)
> +{
> + return PHYS_ADDR_MAX;
> +}
> +
> #define of_match_ptr(_ptr) NULL
> #define of_match_node(_matches, _node) NULL
> #endif /* CONFIG_OF */
> --
> 2.28.0