netdev - Re: [PATCH net-next] net: dsa: mv88e6xxx: Allow dynamic reconfiguration of tag protocol

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Message-ID: <87k0pvlkwe.fsf@waldekranz.com>
Date:   Thu, 25 Mar 2021 09:04:01 +0100
From:   Tobias Waldekranz <tobias@...dekranz.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, andrew@...n.ch,
        vivien.didelot@...il.com, f.fainelli@...il.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: dsa: mv88e6xxx: Allow dynamic reconfiguration of tag protocol

On Thu, Mar 25, 2021 at 03:34, Vladimir Oltean <olteanv@...il.com> wrote:
> On Wed, Mar 24, 2021 at 05:07:09PM +0100, Tobias Waldekranz wrote:
>> But even if the parser was enabled, it would never get anywhere since
>> the Ethertype would look like random garbage. Unless we have the soft
>> parser, but then it is not the middle ground anymore :)
>
> Garbage, true, but garbage with enough entropy to allow for some sort of
> RFS (ideally you can get the source port field from the DSA tag into the
> area covered by the n-tuple on which the master performs hashing). This
> is the way in which the switches inside NXP LS1028A and T1040 work.

I see what you are saying. Any given flow would still have the same
not-really-an-Ethertype.

>> I suppose you would like to test for netdev_uses_dsa_and_violates_8023,
>> that way you could still do RSS on DSA devices using regular 1Q-tags for
>> example. Do we want to add this property to the taggers so that we do
>> not degrade performance for any existing users?
>
> Yes, so T1040 is one such example of device that would be negatively
> affected by this change. There isn't a good solution to solve all
> problems: there will be some Marvell switches which can't operate in
> EDSA mode, and there will be some DSA masters that can't parse Marvell
> DSA tags. Eventually all possible combinations of workarounds will have
> to be implemented. But for now, I think I prefer to see the simplest
> one, which has just become the one based on device tree.

Alright, it seems like everyone agrees then. I will look into it.

Just to avoid a DenverCoder9 situation; I tried changing the NIA in
FMBM_RFNE like you suggested:

8< ---

diff --git a/drivers/net/ethernet/freescale/fman/fman_port.c b/drivers/net/ethernet/freescale/fman/fman_port.c
index d9baac0dbc7d..5aa5b4068f2d 100644
--- a/drivers/net/ethernet/freescale/fman/fman_port.c
+++ b/drivers/net/ethernet/freescale/fman/fman_port.c
@@ -543,7 +543,7 @@ static int init_bmi_rx(struct fman_port *port)
        /* NIA */
        tmp = (u32)cfg->rx_fd_bits << BMI_NEXT_ENG_FD_BITS_SHIFT;
 
-       tmp |= NIA_ENG_HWP;
+       tmp |= NIA_ENG_BMI | NIA_BMI_AC_ENQ_FRAME;
        iowrite32be(tmp, &regs->fmbm_rfne);
 
        /* Parser Next Engine NIA */

8< ---

>From what I can tell, this works as expected. TO_CPUs from port 8 can
ingress the device with this in place.