linux-kernel - Re: [PATCH] drivers/char/mem.c: Add /dev/ioports, supporting 16-bit and 32-bit ports

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Message-ID: <1961979.Xhiud0jvNd@wuerfel>
Date:	Tue, 29 Dec 2015 17:20:08 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Santosh Shukla <santosh.shukla@...aro.org>
Cc:	alex.williamson@...hat.com, "H. Peter Anvin" <hpa@...or.com>,
	josh@...htriplett.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	akpm@...ux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-api@...r.kernel.org, yuanhan.liu@...ux.intel.com,
	Santosh Shukla <sshukla@...sta.com>
Subject: Re: [PATCH] drivers/char/mem.c: Add /dev/ioports, supporting 16-bit and 32-bit ports

On Tuesday 29 December 2015 21:25:15 Santosh Shukla wrote:
> mistakenly added wrong email-id of alex, looping his correct one.
> 
> On 29 December 2015 at 21:23, Santosh Shukla <santosh.shukla@...aro.org> wrote:
> > On 29 December 2015 at 18:58, Arnd Bergmann <arnd@...db.de> wrote:
> >> On Wednesday 23 December 2015 17:04:40 Santosh Shukla wrote:
> >>> On 23 December 2015 at 03:26, Arnd Bergmann <arnd@...db.de> wrote:
> >>> > On Tuesday 22 December 2015, Santosh Shukla wrote:
> >>> >> }
> >>> >>
> >>> >> So I care for /dev/ioport types interface who could do more than byte
> >>> >> data copy to/from user-space. I tested this patch with little
> >>> >> modification and could able to run pmd driver for arm/arm64 case.
> >>> >>
> >>> >> Like to know how to address pci_io region mapping problem for
> >>> >> arm/arm64, in-case /dev/ioports approach is not acceptable or else I
> >>> >> can spent time on restructuring the patch?
> >>> >>
> >>> >
> >>> > For the use case you describe, can't you use the vfio framework to
> >>> > access the PCI BARs?
> >>> >
> >>>
> >>> I looked at file: drivers/vfio/pci/vfio_pci.c, func vfio_pci_map() and
> >>> it look to me that it only maps ioresource_mem pci region, pasting
> >>> code snap:
> >>>
> >>> if (!(pci_resource_flags(pdev, index) & IORESOURCE_MEM))
> >>> return -EINVAL;
> >>> ....
> >>>
> >>> and I want to map ioresource_io pci region for arm platform in my
> >>> use-case. Not sure vfio maps pci_iobar region?
> >>
> >> Mapping I/O BARs is not portable, notably it doesn't work on x86.
> >>
> >> You should be able access them using the read/write interface on
> >> the vfio device.
> >>
> > Right, x86 doesn't care as iopl() could give userspace application
> > direct access to ioports.
> >
> > Also, Alex in other dpdk thread [1] suggested someone to propose io
> > bar mapping in vfio-pci, I guess in particular to non-x86 arch so I
> > started working on it.
> >
> 

So what's wrong with just using the existing read/write API on all
architectures?

	Arnd
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