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

On Tue, Dec 29, 2015 at 9:50 PM, Arnd Bergmann [off-list ref] wrote:

On Tuesday 29 December 2015 21:25:15 Santosh Shukla wrote:

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mistakenly added wrong email-id of alex, looping his correct one.

On 29 December 2015 at 21:23, Santosh Shukla [off-list ref] wrote:

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On 29 December 2015 at 18:58, Arnd Bergmann [off-list ref] wrote:

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On Wednesday 23 December 2015 17:04:40 Santosh Shukla wrote:

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On 23 December 2015 at 03:26, Arnd Bergmann [off-list ref] wrote:

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On Tuesday 22 December 2015, Santosh Shukla wrote:

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}

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?

nothing wrong, infact read/write api will still be used so to access
mmaped io pci bar at userspace. But right now vfio_pci_map() doesn't
map io pci bar in particular (i.e.. ioresource_io) so I guess need to
add that bar mapping in vfio. pl. correct me if i misunderstood
anything.

        Arnd