linux-kernel - Re: [PATCH v2 2/5] of/address: Introduce of_dma_lower_bus

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Date:   Sun, 11 Oct 2020 09:47:06 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-rpi-kernel@...ts.infradead.org,
        Jeremy Linton <jeremy.linton@....com>,
        iommu@...ts.linux-foundation.org,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] of/address: Introduce of_dma_lower_bus_limit()

Hi Nicolas,

$SUBJECT is out of sync with the patch below. Also, for legibility, it
helps if the commit log is intelligible by itself, rather than relying
on $SUBJECT being the first line of the first paragraph.

On Sat, 10 Oct 2020 at 17:12, Nicolas Saenz Julienne
<nsaenzjulienne@...e.de> wrote:
>
> The function provides the CPU physical address addressable by the most
> constrained bus in the system. It might be useful in order to
> dynamically set up memory zones during boot.
>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> ---
>  drivers/of/address.c | 34 ++++++++++++++++++++++++++++++++++
>  include/linux/of.h   |  7 +++++++
>  2 files changed, 41 insertions(+)
>
> diff --git a/drivers/of/address.c b/drivers/of/address.c
> index eb9ab4f1e80b..755e97b65096 100644
> --- a/drivers/of/address.c
> +++ b/drivers/of/address.c
> @@ -1024,6 +1024,40 @@ int of_dma_get_range(struct device_node *np, const struct bus_dma_region **map)
>  }
>  #endif /* CONFIG_HAS_DMA */
>
> +/**
> + * of_dma_safe_phys_limit - Get system wide DMA safe address space
> + *
> + * Gets the CPU physical address limit for safe DMA addressing system wide by
> + * searching for the most constraining dma-range. Otherwise it returns ~0ULL.
> + */
> +u64 __init of_dma_safe_phys_limit(void)

I don't think 'safe' strikes the right tone here. You are looking for
the highest CPU address that is addressable by all DMA masters in the
system.

Something like

of_dma_get_max_cpu_address(void)

perhaps? Also, since this is generic code, phys_addr_t is probably a
better type to return.


> +{
> +       struct device_node *np = NULL;
> +       struct of_range_parser parser;
> +       const __be32 *ranges = NULL;

I think you can drop these NULL initializers.

> +       u64 phys_dma_limit = ~0ULL;

PHYS_ADDR_MAX

> +       struct of_range range;
> +       int len;
> +
> +       for_each_of_allnodes(np) {
> +               dma_addr_t cpu_end = 0;
> +
> +               ranges = of_get_property(np, "dma-ranges", &len);
> +               if (!ranges || !len)
> +                       continue;
> +
> +               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 (phys_dma_limit > cpu_end)
> +                       phys_dma_limit = cpu_end;
> +       }
> +
> +       return phys_dma_limit;
> +}
> +
>  /**
>   * 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..958c64cffa92 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);
>
> +u64 of_dma_safe_phys_limit(void);
> +
>  #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 u64 of_dma_safe_phys_limit(void)
> +{
> +       return ~0ULL;
> +}
> +
>  #define of_match_ptr(_ptr)     NULL
>  #define of_match_node(_matches, _node) NULL
>  #endif /* CONFIG_OF */
> --
> 2.28.0
>