Re: [dpdk-dev] [RFC PATCH] igb_uio: issue FLR during open and release of device file

[Shijith Thotton <shijith.thotton@caviumnetworks.com>]

On Wed, May 31, 2017 at 06:11:40PM +0100, Ferruh Yigit wrote:
> On 5/31/2017 4:30 PM, Stephen Hemminger wrote:
> > On Wed, 31 May 2017 13:20:08 +0100
> > Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> > 
> >> On 5/31/2017 12:09 PM, Shijith Thotton wrote:
> >>> Set UIO info device file operations open and release. Call pci reset
> >>> function inside open and release to clear device state at start and
> >>> end. Copied this behaviour from vfio_pci kernel module code. With this
> >>> change, it is not mandatory to issue FLR by PMD's during init and close.  
> >>
> >> Cc: Jianfeng Tan <jianfeng.tan@intel.com>
> >>
> >> Jianfeng also implemented following patch:
> >> http://dpdk.org/dev/patchwork/patch/17495/
> >>
> >> Which also implements release and open ops, for slightly different
> >> reason (prevent DMA access after app exit), but mainly both are to
> >> gracefully handle application exit status.
> >>
> >> btw, for Jianfeng's case, can adding pci_clear_master() in release and
> >> moving pci_set_master() to open help preventing unwanted DMA?
> >>
> >>
> >> Gregory,
> >>
> >> Can you please check if this patch fixes your issue?
> >>
> >> Thanks,
> >> ferruh
> > 
> > pci_reset should stop all DMA. It also clears master status.

Per Alex Williamson[1], bus master will be disabled after FLR. But a disable is
preferred after reset, since all device won't behave as per spec.

1. http://www.spinics.net/lists/kvm/msg115715.html

> 
> If so, should open() call pci_set_master(), currently it has been only
> called by igbuio_pci_probe() once?

DPDK has pci_uio_set_bus_master/pci_vfio_set_bus_master to set bus master.
Can we leave it to the application ? vfio leaves the device with bus master
disabled after open.