netdev - Re: [PATCH v8 net-next 10/14] pds_core: add auxiliary

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Date:   Wed, 5 Apr 2023 10:17:03 -0700
From:   Shannon Nelson <shannon.nelson@....com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     brett.creeley@....com, davem@...emloft.net, netdev@...r.kernel.org,
        kuba@...nel.org, drivers@...sando.io, jiri@...nulli.us
Subject: Re: [PATCH v8 net-next 10/14] pds_core: add auxiliary_bus devices

On 4/4/23 11:07 PM, Leon Romanovsky wrote:
> 
> On Tue, Apr 04, 2023 at 02:44:34PM -0700, Shannon Nelson wrote:
>> On 4/2/23 11:18 PM, Leon Romanovsky wrote:
>>>
>>> On Sat, Apr 01, 2023 at 01:15:03PM -0700, Shannon Nelson wrote:
>>>> On 4/1/23 11:27 AM, Leon Romanovsky wrote:
>>>>>
>>>>> On Thu, Mar 30, 2023 at 04:46:24PM -0700, Shannon Nelson wrote:
>>>>>> An auxiliary_bus device is created for each vDPA type VF at VF probe
>>>>>> and destroyed at VF remove.  The VFs are always removed on PF remove, so
>>>>>> there should be no issues with VFs trying to access missing PF structures.
>>>>>>
>>>>>> Signed-off-by: Shannon Nelson <shannon.nelson@....com>
>>>>>> ---
>>>>>>     drivers/net/ethernet/amd/pds_core/Makefile |   1 +
>>>>>>     drivers/net/ethernet/amd/pds_core/auxbus.c | 142 +++++++++++++++++++++
>>>>>>     drivers/net/ethernet/amd/pds_core/core.h   |   6 +
>>>>>>     drivers/net/ethernet/amd/pds_core/main.c   |  36 +++++-
>>>>>>     include/linux/pds/pds_auxbus.h             |  16 +++
>>>>>>     include/linux/pds/pds_common.h             |   1 +
>>>>>>     6 files changed, 200 insertions(+), 2 deletions(-)
>>>>>>     create mode 100644 drivers/net/ethernet/amd/pds_core/auxbus.c
>>>>>>     create mode 100644 include/linux/pds/pds_auxbus.h
>>>>>
>>>>> I feel that this auxbus usage is still not correct.
>>>>>
>>>>> The idea of auxiliary devices is to partition physical device (for
>>>>> example PCI device) to different sub-devices, where every sub-device
>>>>> belongs to different sub-system. It is not intended to create per-VF
>>>>> devices.
>>>>>
>>>>> In your case, you should create XXX vDPA auxiliary devices which are
>>>>> connected in one-to-one scheme to their PCI VF counterpart.
>>>>
>>>> I don't understand - first I read
>>>>       "It is not intended to create per-VF devices"
>>>> and then
>>>>       "you should create XXX vDPA auxiliary devices which are
>>>>       connected in one-to-one scheme to their PCI VF counterpart."
>>>> These seem at first to be directly contradictory statements, so maybe I'm
>>>> missing some nuance.
>>>
>>> It is not, as I'm looking in the code and don't expect to see the code
>>> like this. It gives me a sense that auxdevice is not created properly
>>> as nothing shouldn't be happen from these checks.
>>>
>>> +       if (pf->state) {
>>> +               dev_warn(vf->dev, "%s: PF in a transition state (%lu)\n",
>>> +                        __func__, pf->state);
>>> +               err = -EBUSY;
>>> +       } else if (!pf->vfs) {
>>> +               dev_warn(vf->dev, "%s: PF vfs array not ready\n",
>>> +                        __func__);
>>> +               err = -ENOTTY;
>>> +       } else if (vf->vf_id >= pf->num_vfs) {
>>> +               dev_warn(vf->dev, "%s: vfid %d out of range\n",
>>> +                        __func__, vf->vf_id);
>>> +               err = -ERANGE;
>>> +       } else if (pf->vfs[vf->vf_id].padev) {
>>> +               dev_warn(vf->dev, "%s: vfid %d already running\n",
>>> +                        __func__, vf->vf_id);
>>> +               err = -ENODEV;
>>> +       }
>>>
>>>>
>>>> We have a PF device that has an adminq, VF devices that don't have an
>>>> adminq, and the adminq is needed for some basic setup before the rest of the
>>>> vDPA driver can use the VF.  To access the PF's adminq we set up an
>>>> auxiliary device per feature in each VF - but currently only offer one
>>>> feature (vDPA) and no sub-devices yet.  We're trying to plan for the future.
>>>
>>> It looks like premature effort to me.
>>>
>>>>
>>>> Is it that we only have one feature per VF so far is what is causing the
>>>> discomfort?
>>>
>>> This whole patch is not easy for me.
>>
>> Yes, those are extraneous checks left from testing the new driver
>> organization.  They are no longer needed, and can come out in the next
>> round.
>>
>> In addition to spreading out the pds_core.rst creation across the patchset
>> and adding more to the commit descriptions, I'll see if there are some other
>> nips and tucks I can do to possibly make the patchset more palatable.
> 
> You also need to rework your auxdevice id creation scheme to be more
> like other drivers.
> 
> This line assumes that you have only one PF device in the system.
> +       aux_dev->id = vf->id;
> 

Yes, that really should be an ida_alloc(), thanks.
sln