Re: [dpdk-dev] [RFC] igb_uio: deprecate iomem and ioport mapping

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

Hi Stephen,

> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Saturday, December 3, 2016 7:47 AM
> To: Tan, Jianfeng
> Cc: dev@dpdk.org; david.marchand@6wind.com; Yigit, Ferruh
> Subject: Re: [RFC] igb_uio: deprecate iomem and ioport mapping
> 
> On Thu,  1 Sep 2016 02:16:37 +0000
> Jianfeng Tan <jianfeng.tan@intel.com> wrote:
> 
> > Previously in igb_uio, iomem is mapped, and both ioport and io mem
> > are recorded into uio framework, which is duplicated and makes the
> > code too complex.
> >
> > For iomem, DPDK user space code never opens or reads files under
> > /sys/pci/bus/devices/xxxx:xx:xx.x/uio/uioY/maps/. Instead,
> > /sys/pci/bus/devices/xxxx:xx:xx.x/resourceY are used to map device
> > memory.
> >
> > For ioport, non-x86 platforms cannot read from files under
> > /sys/pci/bus/devices/xxxx:xx:xx.x/uio/uioY/portio/ directly, because
> > non-x86 platforms need to map port region for access in user space,
> > see non-x86 version pci_uio_ioport_map(). x86 platforms can use the
> > the same way as uio_pci_generic.
> >
> > This patch deprecates iomem and ioport mapping in igb_uio kernel
> > module, and adjusts the iomem implementation in both igb_uio and
> > uio_pci_generic:
> >   - for x86 platform, get ports info from /proc/ioports;
> >   - for non-x86 platform, map and get ports info by pci_uio_ioport_map().
> >
> > Note: this will affect those applications who are using files under
> > /sys/pci/bus/devices/xxxx:xx:xx.x/uio/uioY/maps/ and
> > /sys/pci/bus/devices/xxxx:xx:xx.x/uio/uioY/portio/.
> >
> > Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> 
> What about people using older kernels with the new DPDK EAL and
> vice versa? 

There are two things planned in this proposal:
(1) deprecating iomem mapping in igb_uio, which is not used in DPDK code anyway.
(2) deprecating ioport mapping in igb_uio, which has effect on ioport mapping for x86 platforms. The way we use to make up is to leverage how uio_pci_generic does, aka, based on /proc/ioports, and this proc file is available at very early stage of Linux (Even before 2.6.32).

So I don't see a problem there when running the new DPDK EAL on older kernels.

On the other way, running old DPDK EAL on new kernels, and using new igb_uio, right? Oops, this should have problem. Thank you for pointing out this. So how about just removing iomem? And my motivation to clean igb_uio like this way is to fix a problem here: http://dpdk.org/dev/patchwork/patch/17495/.

> It makes sense to make igb_uio generic for non DPDK
> usage, so it should probably follow the other UIO drivers.
> 

Then the problem would be backward compatibility. I might need to reconsider this.

Thank you for reviewing!

Thanks,
Jianfeng