RE: [PATCH v1] raw/ifpga: remove virtual device unplug operation

["Huang, Wei" <wei.huang@intel.com>]

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Thursday, March 23, 2023 16:52
> To: Huang, Wei <wei.huang@intel.com>
> Cc: dev@dpdk.org; david.marchand@redhat.com; stable@dpdk.org; Xu,
> Rosen <rosen.xu@intel.com>; Zhang, Tianfei <tianfei.zhang@intel.com>;
> Zhang, Qi Z <qi.z.zhang@intel.com>
> Subject: Re: [PATCH v1] raw/ifpga: remove virtual device unplug operation
> 
> 23/03/2023 04:26, Huang, Wei:
> > From: Thomas Monjalon <thomas@monjalon.net>
> > > 22/03/2023 02:26, Huang, Wei:
> > > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > > 21/03/2023 09:41, Huang, Wei:
> > > > > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > > > > 21/03/2023 01:11, Huang, Wei:
> > > > > > > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > > > > > > 16/03/2023 21:44, Wei Huang:
> > > > > > > > > > VDEV bus has implemented cleanup() function to perform
> > > > > > > > > > cleanup for devices on the bus during eal_cleanup(),
> > > > > > > > > > so there is no need for ifpga driver to record virtual
> > > > > > > > > > devices and
> > > unplug them.
> > > > > > > > >
> > > > > > > > > Why no need?
> > > > > > > > > If the application wants to explicitly remove a device,
> > > > > > > > > what
> > > happens?
> > > > > > > > >
> > > > > > > > >
> > > > > > > > EAL will output an error information "Cannot find plugged
> > > > > > > > device
> > > (%s)".
> > > > > > >
> > > > > > > It does not look what we expect.
> > > > > > >
> > > > > > Let me clear it.
> > > > > > With this patch, no error information will be outputted.
> > > > > > Without this patch, error information will be outputted.
> > > > > > Because bus cleanup action will unplug virtual device, then
> > > > > > ifpga PMD unplug the virtual device which is already be
> > > > > > cleanup,
> > > > >
> > > > > Why ipfga unplug the device after the bus cleanup?
> > > > > I'm not following.
> > > > >
> > > > The virtual device is created upon ifpga, if VDEV bus doesn't
> > > > perform cleanup, ifpga has the responsibility to unplug these virtual
> devices.
> > >
> > > Really I don't understand the flow.
> > > Are you talking about EAL cleanup case?
> > Yes, it's about EAL cleanup.
> > > What happens first? Do you need ifpga to be called first?
> > The cleanup flow is rte_eal_cleanup() -> eal_bus_cleanup()
> > eal_bus_cleanup() will call each bus's cleanup method to complete cleanup
> work.
> > There are three types of device related to ifpga PMD: PCI device, VDEV
> device and AFU device.
> > VDEV device is created on PCI device, it's a mediate device which purpose
> is to plug a AFU device on IFPGA bus.
> > Before eal_bus_cleanup() is implemented, application will call
> rte_pmd_ifpga_cleanup() to remove PCI device, VDEV device will be
> removed when PCI device is removed, AFU device will be removed when
> VDEV device is removed, it works fine.
> > Now eal_bus_cleanup() takes the job, application has no need to call
> rte_pmd_ifpga_cleanup(), ifpga PCI device has no need to remove ifpga
> VDEV device and ifpga VDEV device has no need to remove ifpga AFU device.
> 
> That's the problem in your approach.
> You need to keep the code removing children devices.
> And if all children are removed, then the parent should remove itself.
> If you implement these 2 conditions, the cleanup can happen in any order.
> 
OK, this patch should be rejected, I will commit another patch according to your comments.
> > > I think you need the correct checks to allow any order of cleanup.
> > When this patch is committed, no order dependent on cleanup.
> >
> > > > > > bus->find_device() returns NULL,
> > > > > > EAL output "Cannot find plugged device (%s)\n" at line 302 in
> > > > > > eal_common_dev.c
> > > > >
> > > > > Anyway, the good answer is not to completely remove the "remove"
> > > > > operation.
> > > > >
> > > > If not to completely remove the "remove", the same virtual device
> > > > will be
> > > unplug twice, is it reasonable?
> > >
> > > You need to add a check to not unplug something already unplugged.
> > > But you must allow the user calling "remove" directly.
> > >
> > rte_pmd_ifpga_cleanup() is the only one interface for user to calling
> > "remove" directly,
> 
> No, there are functions in EAL to "remove" devices, like rte_dev_remove(),
> and we must make sure it works effectively.
> 
> > when this patch is committed, VDEV and AFU device will not be unplugged
> twice.
> > For PCI device, the implementation of rte_pmd_ifpga_cleanup() is like
> below
> > 	for (i = 0; i < IFPGA_RAWDEV_NUM; i++) {
> > 		dev = &ifpga_rawdevices[i];
> > 		if (dev->rawdev) {
> > 			rte_rawdev_pmd_release(dev->rawdev);
> > 			dev->rawdev = NULL;
> > 		}
> > 	}
> > If ifpga PCI device is already removed, dev->rawdev is NULL, it will not be
> unplugged again.
> 
> 
>