Re: [RFT PATCH v3 12/27] of/address: Add infrastructure to declare MMIO as non-posted

[Rob Herring]

On Fri, Mar 5, 2021 at 9:13 AM Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
>
> On Thu, Mar 4, 2021 at 11:40 PM Hector Martin <marcan@xxxxxxxxx> wrote:
> >
> > This implements the 'nonposted-mmio' and 'posted-mmio' boolean
> > properties. Placing these properties in a bus marks all child devices as
> > requiring non-posted or posted MMIO mappings. If no such properties are
> > found, the default is posted MMIO.
> >
> > of_mmio_is_nonposted() performs the tree walking to determine if a given
> > device has requested non-posted MMIO.
> >
> > of_address_to_resource() uses this to set the IORESOURCE_MEM_NONPOSTED
> > flag on resources that require non-posted MMIO.
> >
> > of_iomap() and of_io_request_and_map() then use this flag to pick the
> > correct ioremap() variant.
> >
> > This mechanism is currently restricted to Apple ARM platforms, as an
> > optimization.
>
> ...
>
> > @@ -896,7 +899,10 @@ void __iomem *of_iomap(struct device_node *np, int index)
> >         if (of_address_to_resource(np, index, &res))
> >                 return NULL;
> >
> > -       return ioremap(res.start, resource_size(&res));
> > +       if (res.flags & IORESOURCE_MEM_NONPOSTED)
> > +               return ioremap_np(res.start, resource_size(&res));
> > +       else
> > +               return ioremap(res.start, resource_size(&res));
>
> This doesn't sound right. Why _np is so exceptional? Why don't we have
> other flavours (it also rings a bell to my previous comment that the
> flag in ioresource is not in the right place)?
>
> ...
>
> > +       if (res.flags & IORESOURCE_MEM_NONPOSTED)
> > +               mem = ioremap_np(res.start, resource_size(&res));
> > +       else
> > +               mem = ioremap(res.start, resource_size(&res));
> > +
>
> Ditto.
>
> ...
>
> > +       while (node) {
> > +               if (!of_property_read_bool(node, "ranges")) {
> > +                       break;
> > +               } else if (of_property_read_bool(node, "nonposted-mmio")) {
> > +                       of_node_put(node);
> > +                       return true;
> > +               } else if (of_property_read_bool(node, "posted-mmio")) {
> > +                       break;
> > +               }
> > +               parent = of_get_parent(node);
> > +               of_node_put(node);
> > +               node = parent;
> > +       }
>
> I believe above can be slightly optimized. Don't we have helpers to
> traverse to all parents?

We don't. I only found a handful of cases mostly in arch/powerpc.
Given that and this series is big enough already, I don't think we
need a helper as part of it. But patches welcome.

Rob