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

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Message-ID: <CAL_Jsq+cPQS7836YqVos=n-TFOvc8kXa8ZXGq5_=rZAzz8RLLQ@mail.gmail.com>
Date:   Wed, 14 Oct 2020 07:23:53 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
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 v2 2/5] of/address: Introduce of_dma_lower_bus_limit()

On Wed, Oct 14, 2020 at 6:52 AM Nicolas Saenz Julienne
<nsaenzjulienne@...e.de> wrote:
>
> Hi Rob,
>
> On Mon, 2020-10-12 at 10:25 -0500, Rob Herring wrote:
> > On Sat, Oct 10, 2020 at 10:12 AM 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)
> > > +{
> > > +       struct device_node *np = NULL;
> > > +       struct of_range_parser parser;
> > > +       const __be32 *ranges = NULL;
> > > +       u64 phys_dma_limit = ~0ULL;
> > > +       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;
> >
> > This doesn't work if you have more than one level of dma-ranges. The
> > address has to be translated first. It should be okay to do that on
> > the start or end address (if not, your DT is broken).
>
> for_each_of_range() calls of_pci_range_parser_one() which utimately populates
> range.cpu_addr with of_translate_dma_address() results. Isn't that good enough?

Indeed. I guess I was remembering the cases not using
for_each_of_range which forgot to do that...

Rob