Message-ID: <93abb8d0-40c6-4758-a8de-c79d7acce6bc@broadcom.com>
Date: Fri, 27 Oct 2023 10:15:28 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Jacob Keller <jacob.e.keller@...el.com>, netdev@...r.kernel.org
Cc: Doug Berger <opendmb@...il.com>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
 Russell King <linux@...linux.org.uk>,
 Vladimir Oltean <vladimir.oltean@....com>, Tariq Toukan <tariqt@...dia.com>,
 Gal Pressman <gal@...dia.com>, Willem de Bruijn <willemb@...gle.com>,
 Daniil Tatianin <d-tatianin@...dex-team.ru>, Simon Horman
 <horms@...nel.org>, Justin Chen <justin.chen@...adcom.com>,
 Ratheesh Kannoth <rkannoth@...vell.com>, Joe Damato <jdamato@...tly.com>,
 Vincent Mailhol <mailhol.vincent@...adoo.fr>, Jiri Pirko <jiri@...nulli.us>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2 5/5] net: bcmgenet: Interrogate PHY for
 WAKE_FILTER programming

On 10/27/23 09:55, Jacob Keller wrote:
> 
> 
> On 10/26/2023 4:52 PM, Florian Fainelli wrote:
>> On 10/26/23 16:23, Jacob Keller wrote:
>>>
>>>
>>> On 10/26/2023 3:45 PM, Florian Fainelli wrote:
>>>> Determine whether the PHY can support waking up from the user programmed
>>>> network filter, and if it can utilize it.
>>>>
>>>
>>> Here, you're passing through to phy_ethtool_set_rxnfc, basically
>>> allowing the lower device to program the wakeup filter if its supported. Ok.
>>>
>>> This almost feels like it would belong generally in the higher level
>>> ethtool code rather than in the driver?
>>
>> Agreed, as Doug just pointed out to me, there is still an open question
>> about reconciling the PHY and the MAC RXNFC spaces into a single
>> ethtool_rxnfc structure.
>>
>> An ideal goal is to have zero modifications to neither the MAC or the
>> PHY drivers such that they can both work in their own spaces as if they
>> were alone, or combined.
>>
>> I suppose that if we get the number of supported rules from the MAC
>> first, and then get the supported number of rules from the PHY next, we
>> could do something like this:
>>
>> rule index
>> | 0|
>> | .| -> MAC rules
>> |15|
>> |16| -> PHY rule
>>
>> and each of the MAC or the PHY {get,set}_rxnfc() operate within a base
>> rule number which is relative to their own space. So the MAC driver
>> would continue to care about its (max..first) - base (0) range, and the
>> PHY would care about (max..first) - base (16).
>>
>> Though then the issue is discoverability, how do you know which rule
>> location is backed by which hardware block. We could create an
>> intermediate and inert rule at index 16 for instance that acts as a
>> delimiter?
>>
>> Or we could create yet another RX_CLS_LOC_* value that is "special" and
>> can denote whether of the MAC or the PHY we should be targeting
>> whichever is supported, but that does not usually lend itself to being
>> logically ORed with the existing RX_CLS_LOC_* values. WDYT?
>>
>> pw-bot: cr
> 
> Ah, yea there is a lot of complexity to consider here.

Yes this is only the tip of iceberg! Here is hopefully a better 
description of our particular system where this is being requested (the 
fact there is a single one also makes me question the entire effort, but 
anyway). We have 2 distinct system sleep modes:

- akin to ACPI S2 where the Ethernet PHY and MAC remain enabled and both 
can be used for Wake-on-LAN filtering, with the MAC being more capable 
than the PHY. System power consumption is just around 500mW at the wall. 
In that case it would make sense to leverage the MAC's capability 
because it is better and would lead to fewer false wake-ups

- akin to ACPI S3 where the Ethernet PHY only remains enabled, the MAC 
is powered off (as is most of the SoC), but we have limited Wake-on-LAN 
capability in the form of network filter as we can only match on a 
custom MAC DA + mask. System power consumption is closer to 350mW at the 
wall.

My users are not really willing to use the broad WAKE_MCAST because they 
want to match specifically on mDNS over IPv4 (or IPv6), so they prefer 
to program an exact match to limit the amount of false wake-ups. 
Arguably there will already be quite a lot in home network due to 
phones, IoT devices, and whatnot.

 From an user perspective they would know which system standby state is 
being entered so one could imagine that ahead of entry, we could 
configure either the MAC, or the PHY when targeting S2, or just the PHY 
when targeting S3. This implies that we can selectively target one 
entity, or the other.

For the current time being, and knowing the use case of my users, 
directing all of the Wake-on-LAN configuration towards the PHY would be 
enough IMHO, even if that means we stop leveraging the MAC capabilities, 
hence this patch series.

> 
> I'm not entirely sure what we should do here. What about extending with
> another attribute entirely instead of another bit in RX_CLS_LOC?

Yes possibly, or we just target different objects, right now we have 
visibility into the MACs via the net_device, it seems like we ought to 
be able to target some ethtool APIs towards PHY objects, which currently 
have no netlink representation. There is on-going work to bridge that gap:

https://lore.kernel.org/netdev/ffc6ff4a-d1af-4643-a538-fd13e6be9e06@lunn.ch/T/

but I am not sure we will reach an agreement any time soon. Maybe I can 
convince my masters to wait for that to land and use WAKE_MCAST in the 
meantime.

I would not necessary want to invent a new set of ethtool commands and 
kernel APIs such that we could do the below examples, though maybe this 
is not incompatible with the work being done by Maxime:

# Target the Ethernet MAC
ethtool -N eth0 flow-type ether dst 01:00:5e:00:00:fb loc 0 action -2 # 
Assumes MAC by default
ethtool -N eth0 flow-type ether dst 01:00:5e:00:00:fb loc 0 action -2 
target mac

# Target the Ethernet PHY, if capable
ethtool -N eth0 flow-type ether dst 01:00:5e:00:00:fb loc 0 action -2 
target phy

# Enable WAKE_FILTER at the MAC level
ethtool -s eth0 wol f # assumes MAC by default
ethtool -s eth0 wol f target mac

# Enable WAKE_FILTER at the PHY level, if capable
ethtool -s eth0 wol f target phy

though maybe this is the much needed addition to ethtool so we can be 
more selective.

After a bunch of candies on Tuesday I might reach a state of trance and 
figure which way to proceed :D
-- 
Florian


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