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Date:   Tue, 10 Jan 2017 17:42:23 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Ido Schimmel <idosch@...sch.org>, Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        vivien.didelot@...oirfairelinux.com, andrew@...n.ch
Subject: Re: [PATCH net-next 0/4] net: switchdev: Avoid sleep in atomic with
 DSA

On 01/10/2017 08:08 AM, Ido Schimmel wrote:
> On Tue, Jan 10, 2017 at 03:18:07PM +0100, Jiri Pirko wrote:
>> Tue, Jan 10, 2017 at 02:25:06PM CET, idosch@...sch.org wrote:
>>> On Tue, Jan 10, 2017 at 01:08:46PM +0100, Jiri Pirko wrote:
>>>> Mon, Jan 09, 2017 at 10:14:36PM CET, idosch@...sch.org wrote:
>>>>> On Mon, Jan 09, 2017 at 12:56:48PM -0800, Florian Fainelli wrote:
>>>>>> On 01/09/2017 12:48 PM, Ido Schimmel wrote:
>>>>>>> Hi Florian,
>>>>>>>
>>>>>>> On Mon, Jan 09, 2017 at 11:44:59AM -0800, Florian Fainelli wrote:
>>>>>>>> Hi all,
>>>>>>>>
>>>>>>>> This patch series is to resolve a sleeping function called in atomic context
>>>>>>>> debug splat that we observe with DSA.
>>>>>>>>
>>>>>>>> Let me know what you think, I was also wondering if we should just always
>>>>>>>> make switchdev_port_vlan_fill() set SWITCHDEV_F_DEFER, but was afraid this
>>>>>>>> could cause invalid contexts to be used for rocker, mlxsw, i40e etc.
>>>>>>>
>>>>>>> Isn't this a bit of overkill? All the drivers you mention fill the VLAN
>>>>>>> dump from their cache and don't require sleeping. Even b53 that you
>>>>>>> mention in the last patch does that, but reads the PVID from the device,
>>>>>>> which entails taking a mutex.
>>>>>>
>>>>>> Correct.
>>>>>>
>>>>>>>
>>>>>>> Can't you just cache the PVID as well? I think this will solve your
>>>>>>> problem. Didn't look too much into the b53 code, so maybe I'm missing
>>>>>>> something. Seems that mv88e6xxx has a similar problem.
>>>>>>
>>>>>> I suppose we could indeed cache the PVID for b53, but for mv88e6xxx it
>>>>>> seems like we need to perform a bunch of VTU operations, and those
>>>>>> access HW registers, Andrew, Vivien, how do you want to solve that, do
>>>>>> we want to introduce a general VLAN cache somewhere in switchdev/DSA/driver?
>>>>>
>>>>> Truth be told, I don't quite understand why switchdev infra even tries
>>>>> to dump the VLANs from the device. Like, in which situations is this
>>>>> going to be different from what the software bridge reports? Sure, you
>>>>> can set the VLAN filters with SELF and skip the software bridge, but how
>>>>> does that make sense in a model where you want to reflect the software
>>>>> datapath?
>>>>
>>>> But the vlans added by rtnl_bridge_setlink & SELF are not tracked by the
>>>> bridge and therefore driver needs to dump them. You would have to pass
>>>> some flag down to driver when adding SWITCHDEV_OBJ_ID_PORT_VLAN
>>>> indicating the need to track the vlan and dump it. Right?
>>>
>>> Right, but back to my question - what's the use case for the SELF flag
>>> in the switchdev model? Why would I configure a VLAN filter in the
>>> hardware but not in the software bridge? The whole point is reflecting
>>> the software bridge to the hardware.
>>
>> I agree. For the bridge-switchdev usecase, I don't see a reason to use
>> SELF for vlans as well. Do you suggest to simply remove this possibility?
> 
> Yes. This would also solve Florian's problem.
> 
> Florian, what do you think?

I don't really see a value for configuring a VLAN in HW exclusively and
not at the SW bridge level as well (unless you wanted some kind of
discarding of packets?). Even with the patch proposed a while back to
decouple the bridge master device, we would still end up with the same
VLAN attributes programmed in HW and SW.

Vivien, Andrew, are you aware of an use case where we have the HW
programmed with a superset of VLANs wrt. the SW bridge?
-- 
Florian

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