Re: [PATCH v2 2/5] of/address: Introduce of_dma_lower_bus_limit()

[Nicolas Saenz Julienne]

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@xxxxxxx> 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@xxxxxxx>
> > ---
> >  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?

> Please add/extend a unittest for this.

Will do.

Regards,
Nicolas

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