linux-kernel - Re: [PATCH v3 3/8] of/address: Introduce of_dma_get_max_cpu

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Date:   Thu, 15 Oct 2020 10:54:11 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Christoph Hellwig <hch@....de>,
        Ard Biesheuvel <ardb@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        Jeremy Linton <jeremy.linton@....com>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v3 3/8] of/address: Introduce
 of_dma_get_max_cpu_address()

On Wed, 2020-10-14 at 17:02 -0500, Rob Herring wrote:
> On Wed, Oct 14, 2020 at 2:12 PM Nicolas Saenz Julienne
> <nsaenzjulienne@...e.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@...e.de>
> > 
> > ---

[...]

> > +       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?

Yes, it's a little more complex. But I had to change it in order to be able to
start parsing down from an arbitrary device node, which is needed for the unit
tests.

for_each_of_allnodes() and friends will traverse the whole tree, regardless of
the starting point. I couldn't find a similar function that would just iterate
over a subsection of the tree, so I went with this recursive approach.

Regards,
Nicolas


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