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From: Ard Biesheuvel <ardb@kernel.org>
To: Rob Herring <robh+dt@kernel.org>
Cc: "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Jeremy Linton <jeremy.linton@arm.com>,
	Linux IOMMU <iommu@lists.linux-foundation.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Christoph Hellwig <hch@lst.de>,
	"moderated list:BROADCOM BCM2835 ARM ARCHITECTURE"
	<linux-rpi-kernel@lists.infradead.org>
Subject: Re: [PATCH v3 3/8] of/address: Introduce of_dma_get_max_cpu_address()
Date: Thu, 15 Oct 2020 08:56:40 +0200
Message-ID: <CAMj1kXFnLEpNTZVq16YgBomkZwwdGsH89OSELsYeiee4P+GLPg@mail.gmail.com> (raw)
In-Reply-To: <CAL_JsqKMGSCTmKF2Lt8GQFx0DVFFH1bLVBw=bRDM7upahGvKDQ@mail.gmail.com>

On Thu, 15 Oct 2020 at 00:03, Rob Herring <robh+dt@kernel.org> wrote:
>
> 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.
>

PHYS_ADDR_MAX is the max addressable CPU address on the system, and so
it makes sense to use it for the return type, and for the preliminary
return value: this is actually what /prevents/ truncation, because we
will only overwrite max_cpu_addr if the new u64 value is lower.


> > +       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
> >
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Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-14 19:12 [PATCH v3 0/8] arm64: Default to 32-bit wide ZONE_DMA Nicolas Saenz Julienne
2020-10-14 19:12 ` [PATCH v3 1/8] arm64: mm: Move reserve_crashkernel() into mem_init() Nicolas Saenz Julienne
2020-10-15  8:40   ` Will Deacon
2020-10-15  8:55     ` Nicolas Saenz Julienne
2020-10-14 19:12 ` [PATCH v3 2/8] arm64: mm: Move zone_dma_bits initialization into zone_sizes_init() Nicolas Saenz Julienne
2020-10-14 19:12 ` [PATCH v3 3/8] of/address: Introduce of_dma_get_max_cpu_address() Nicolas Saenz Julienne
2020-10-14 22:02   ` Rob Herring
2020-10-15  6:56     ` Ard Biesheuvel [this message]
2020-10-15  9:16       ` Nicolas Saenz Julienne
2020-10-15  9:18         ` Ard Biesheuvel
2020-10-15  8:54     ` Nicolas Saenz Julienne
2020-10-15  5:42   ` Christoph Hellwig
2020-10-15 10:03     ` Nicolas Saenz Julienne
2020-10-16 13:19     ` Rob Herring
2020-10-14 19:12 ` [PATCH v3 4/8] of: unittest: Add test for of_dma_get_max_cpu_address() Nicolas Saenz Julienne
2020-10-14 22:04   ` Rob Herring
2020-10-15  9:51     ` Nicolas Saenz Julienne
2020-10-14 19:12 ` [PATCH v3 5/8] dma-direct: Turn zone_dma_bits default value into a define Nicolas Saenz Julienne
2020-10-15  5:38   ` Christoph Hellwig
2020-10-15 10:05     ` Nicolas Saenz Julienne
2020-10-14 19:12 ` [PATCH v3 6/8] arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges Nicolas Saenz Julienne
2020-10-15  5:39   ` Christoph Hellwig
2020-10-15 10:05     ` Nicolas Saenz Julienne
2020-10-14 19:12 ` [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan Nicolas Saenz Julienne
2020-10-15 10:31   ` Lorenzo Pieralisi
2020-10-16  6:56     ` Ard Biesheuvel
2020-10-15 14:26   ` Hanjun Guo
2020-10-15 15:15     ` Nicolas Saenz Julienne
2020-10-15 18:03     ` Catalin Marinas
2020-10-16  6:51       ` Hanjun Guo
2020-10-16  6:54         ` Ard Biesheuvel
2020-10-16  7:27           ` Hanjun Guo
2020-10-16  7:34             ` Hanjun Guo
2020-10-14 19:12 ` [PATCH v3 8/8] mm: Update DMA zones description Nicolas Saenz Julienne
2020-10-15  5:40   ` Christoph Hellwig

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