linux-kernel - Re: [PATCH v4 0/6] Add Auxiliary driver support

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Date:   Mon, 14 Nov 2022 16:47:31 -0800
From:   Ajit Khaparde <ajit.khaparde@...adcom.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     andrew.gospodarek@...adcom.com, davem@...emloft.net,
        edumazet@...gle.com, jgg@...pe.ca, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        michael.chan@...adcom.com, netdev@...r.kernel.org,
        pabeni@...hat.com, selvin.xavier@...adcom.com
Subject: Re: [PATCH v4 0/6] Add Auxiliary driver support

Leon,
We appreciate your valuable feedback.
Please see inline.

On Thu, Nov 10, 2022 at 2:53 AM Leon Romanovsky <leon@...nel.org> wrote:
>
> On Wed, Nov 09, 2022 at 10:42:38AM -0800, Ajit Khaparde wrote:
> > Add auxiliary device driver for Broadcom devices.
> > The bnxt_en driver will register and initialize an aux device
> > if RDMA is enabled in the underlying device.
> > The bnxt_re driver will then probe and initialize the
> > RoCE interfaces with the infiniband stack.
> >
> > We got rid of the bnxt_en_ops which the bnxt_re driver used to
> > communicate with bnxt_en.
> > Similarly  We have tried to clean up most of the bnxt_ulp_ops.
> > In most of the cases we used the functions and entry points provided
> > by the auxiliary bus driver framework.
> > And now these are the minimal functions needed to support the functionality.
> >
> > We will try to work on getting rid of the remaining if we find any
> > other viable option in future.
>
> I still see extra checks for something that was already checked in upper
> functions, for example in bnxt_re_register_netdev() you check rdev, which
> you already checked before.
Sure. I will do another sweep and clean up.

>
> However, the most important part is still existence of bnxt_ulp_ops,
> which shows completely no-go thing - SR-IOV config in RDMA code.
>
>    302 static struct bnxt_ulp_ops bnxt_re_ulp_ops = {
>    303         .ulp_sriov_config = bnxt_re_sriov_config,
>    304         .ulp_irq_stop = bnxt_re_stop_irq,
>    305         .ulp_irq_restart = bnxt_re_start_irq
>    306 };
>
> All PCI management logic and interfaces are needed to be inside eth part
> of your driver and only that part should implement SR-IOV config. Once
> user enabled SR-IOV, the PCI driver should create auxiliary devices for
> each VF. These device will have RDMA capabilities and it will trigger RDMA
> driver to bind to them.
I agree and once the PF creates the auxiliary devices for the VF, the RoCE
Vf indeed get probed and created. But the twist in bnxt_en/bnxt_re
design is that
the RoCE driver is responsible for making adjustments to the RoCE resources.

So once the VF's are created and the bnxt_en driver enables SRIOV adjusts the
NIC resources for the VF,  and such, it tries to call into the bnxt_re
driver for the
same purpose.

1. We do something like this to the auxiliary_device structure:

diff --git a/include/linux/auxiliary_bus.h b/include/linux/auxiliary_bus.h
index de21d9d24a95..4e581fbf458f 100644
--- a/include/linux/auxiliary_bus.h
+++ b/include/linux/auxiliary_bus.h
@@ -148,6 +148,7 @@ struct auxiliary_device {
  * @shutdown: Called at shut-down time to quiesce the device.
  * @suspend: Called to put the device to sleep mode. Usually to a power state.
  * @resume: Called to bring a device from sleep mode.
+ * @sriov_configure: Called to allow configuration of VFs .
  * @name: Driver name.
  * @driver: Core driver structure.
  * @id_table: Table of devices this driver should match on the bus.
@@ -183,6 +184,7 @@ struct auxiliary_driver {
        void (*shutdown)(struct auxiliary_device *auxdev);
        int (*suspend)(struct auxiliary_device *auxdev, pm_message_t state);
        int (*resume)(struct auxiliary_device *auxdev);
+       int (*sriov_configure)(struct auxiliary_device *auxdev, int
num_vfs); /* On PF */
        const char *name;
        struct device_driver driver;
        const struct auxiliary_device_id *id_table;

Then the bnxt_en driver could call into bnxt_re via that interface.

Please let me know what you feel.

2. While it may take care of the first function in the ulp_ops, it
leaves us with two.
And that is where I will need some input if we need to absolutely get
rid of the ops.

2a. We may be able to use the auxiliary_device suspend & resume with a
private flag
in the driver's aux_dev pointer.
2b. Or just like (1) above, add another hook to auxiliary_driver
void (*restart)(struct auxiliary_device *auxdev);
And then use the auxiliary_driver shutdown & restart with a private flag.

Note that we may get creative right now and get rid of the ulp_ops.
But the bnxt_en driver having a need to update the bnxt_re driver is a
part of the
design. So it will help if we can consider beyond the ulp_irq_stop,
ulp_irq_restart.
2c. Maybe keep the bnxt_ulp_ops for that reason?

Thank you for your time.

Thanks
Ajit

>
> Thanks

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