linux-kernel - Re: [PATCH v4 2/3] lib: logic_pio: Reject accesses to unregistered CPU MMIO regions

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Message-ID: <CAK8P3a0C010LEs3HmyQKHWx4EVpVH1NUtFwYkoF16syFQ9hd8w@mail.gmail.com>
Date:   Thu, 13 Jun 2019 09:47:51 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     John Garry <john.garry@...wei.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-pci <linux-pci@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Will Deacon <will.deacon@....com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Linuxarm <linuxarm@...wei.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v4 2/3] lib: logic_pio: Reject accesses to unregistered
 CPU MMIO regions

On Thu, Jun 13, 2019 at 5:20 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Tue, Jun 11, 2019 at 10:12:53PM +0800, John Garry wrote:
> > Currently when accessing logical indirect PIO addresses in
> > logic_{in, out}{,s}, we first ensure that the region is registered.
>
> I think logic_pio is specifically concerned with I/O port space, so
> it's a little bit unfortunate that we named this "PIO".
>
> PIO is a general term for "Programmed I/O", which just means the CPU
> is involved in each transfer, as opposed to DMA.  The transfers can be
> to either MMIO or I/O port space.
>
> So this ends up being a little confusing because I think you mean
> "Port I/O", not "Programmed I/O".

I think the terms that John uses are more common: I would also
assume that "PIO" (regardless of whether you expand it as Port
or Programmed I/O) refers only to inb/outb and PCI/ISA/LPC
I/O space, and is distinct from "MMIO", which refers to the readl/writel
accessors and PCI memory space.

That is consistent with the usage across at least the x86, powerpc
and ia64 architectures when they refer to PIO.

        Arnd