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

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Date:   Fri, 5 Mar 2021 17:13:36 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Hector Martin <marcan@...can.st>
Cc:     linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <maz@...nel.org>, Rob Herring <robh@...nel.org>,
        Arnd Bergmann <arnd@...nel.org>,
        Olof Johansson <olof@...om.net>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Tony Lindgren <tony@...mide.com>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Stan Skowronek <stan@...ellium.com>,
        Alexander Graf <graf@...zon.com>,
        Will Deacon <will@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Hellwig <hch@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Documentation List <linux-doc@...r.kernel.org>,
        Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFT PATCH v3 12/27] of/address: Add infrastructure to declare
 MMIO as non-posted

On Thu, Mar 4, 2021 at 11:40 PM Hector Martin <marcan@...can.st> 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?

-- 
With Best Regards,
Andy Shevchenko