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

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Date:	Tue, 29 Dec 2015 14:28:01 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Santosh Shukla <santosh.shukla@...aro.org>
Cc:	"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
Subject: Re: [PATCH] drivers/char/mem.c: Add /dev/ioports, supporting 16-bit and 32-bit ports

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.

	Arnd
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