linux-kernel - Re: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select it as necessary

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Date:   Fri, 6 May 2022 14:16:56 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Arnd Bergmann <arnd@...nel.org>
cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
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        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
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        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
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Subject: Re: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select
 it as necessary

On Fri, 6 May 2022, Arnd Bergmann wrote:

> >  So what happens if the instruction is given an I/O rather than memory BAR
> > as the relevant argument?  Is the address space indicator bit (bit #0)
> > simply ignored or what?
> 
> Not sure. My best guess is that it would actually work as you'd expect,
> but is deliberately left out of the architecture specification so they don't
> have to to validate the correctness.  Note that only a small number of
> PCIe cards are actually supported by IBM, and I think the firmware
> only passes devices to the OS if they are whitelisted.

 That makes sense, thanks!

  Maciej