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

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Date:   Tue, 9 Mar 2021 08:48:17 -0700
From:   Rob Herring <robh@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Hector Martin <marcan@...can.st>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <maz@...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>,
        Andy Shevchenko <andy.shevchenko@...il.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>,
        DTML <devicetree@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFT PATCH v3 12/27] of/address: Add infrastructure to declare
 MMIO as non-posted

On Mon, Mar 8, 2021 at 2:56 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> On Mon, Mar 8, 2021 at 10:14 PM Rob Herring <robh@...nel.org> wrote:
> > On Mon, Mar 08, 2021 at 09:29:54PM +0100, Arnd Bergmann wrote:
> > > On Mon, Mar 8, 2021 at 4:56 PM Rob Herring <robh@...nel.org> wrote:
> >
> > Let's just stick with 'nonposted-mmio', but drop 'posted-mmio'. I'd
> > rather know if and when we need 'posted-mmio'. It does need to be added
> > to the DT spec[1] and schema[2] though (GH PRs are fine for both).
>
> I think the reason for having "posted-mmio" is that you cannot properly
> define the PCI host controller nodes on the M1 without that: Since
> nonposted-mmio applies to all child nodes, this would mean the PCI
> memory space gets declared as nonposted by the DT, but the hardware
> requires it to be mapped as posted.

I don't think so. PCI devices wouldn't use any of the code paths in
this patch. They would map their memory space with plain ioremap()
which is posted.

Rob