[PATCH net v2] net: ti: icssg-prueth: Fix buffer allocation for ICSSG

[Simon Horman]

On Thu, Jul 10, 2025 at 06:42:50PM +0530, Himanshu Mittal wrote:
> Fixes overlapping buffer allocation for ICSSG peripheral
> used for storing packets to be received/transmitted.
> There are 3 buffers:
> 1. Buffer for Locally Injected Packets
> 2. Buffer for Forwarding Packets
> 3. Buffer for Host Egress Packets
> 
> In existing allocation buffers for 2. and 3. are overlapping causing packet
> corruption.
> 
> Packet corruption observations:
> During tcp iperf testing, due to overlapping buffers the received ack
> packet overwrites the packet to be transmitted. So, we see packets on wire
> with the ack packet content inside the content of next TCP packet from
> sender device.
> 
> Details for AM64x switch mode:
> -> Allocation by existing driver:
> +---------+-------------------------------------------------------------+
> |         |          SLICE 0             |          SLICE 1             |
> |         +------+--------------+--------+------+--------------+--------+
> |         | Slot | Base Address | Size   | Slot | Base Address | Size   |
> |---------+------+--------------+--------+------+--------------+--------+
> |         | 0    | 70000000     | 0x2000 | 0    | 70010000     | 0x2000 |
> |         | 1    | 70002000     | 0x2000 | 1    | 70012000     | 0x2000 |
> |         | 2    | 70004000     | 0x2000 | 2    | 70014000     | 0x2000 |
> | FWD     | 3    | 70006000     | 0x2000 | 3    | 70016000     | 0x2000 |
> | Buffers | 4    | 70008000     | 0x2000 | 4    | 70018000     | 0x2000 |
> |         | 5    | 7000A000     | 0x2000 | 5    | 7001A000     | 0x2000 |
> |         | 6    | 7000C000     | 0x2000 | 6    | 7001C000     | 0x2000 |
> |         | 7    | 7000E000     | 0x2000 | 7    | 7001E000     | 0x2000 |
> +---------+------+--------------+--------+------+--------------+--------+
> |         | 8    | 70020000     | 0x1000 | 8    | 70028000     | 0x1000 |
> |         | 9    | 70021000     | 0x1000 | 9    | 70029000     | 0x1000 |
> |         | 10   | 70022000     | 0x1000 | 10   | 7002A000     | 0x1000 |
> | Our     | 11   | 70023000     | 0x1000 | 11   | 7002B000     | 0x1000 |
> | LI      | 12   | 00000000     | 0x0    | 12   | 00000000     | 0x0    |
> | Buffers | 13   | 00000000     | 0x0    | 13   | 00000000     | 0x0    |
> |         | 14   | 00000000     | 0x0    | 14   | 00000000     | 0x0    |
> |         | 15   | 00000000     | 0x0    | 15   | 00000000     | 0x0    |
> +---------+------+--------------+--------+------+--------------+--------+
> |         | 16   | 70024000     | 0x1000 | 16   | 7002C000     | 0x1000 |
> |         | 17   | 70025000     | 0x1000 | 17   | 7002D000     | 0x1000 |
> |         | 18   | 70026000     | 0x1000 | 18   | 7002E000     | 0x1000 |
> | Their   | 19   | 70027000     | 0x1000 | 19   | 7002F000     | 0x1000 |
> | LI      | 20   | 00000000     | 0x0    | 20   | 00000000     | 0x0    |
> | Buffers | 21   | 00000000     | 0x0    | 21   | 00000000     | 0x0    |
> |         | 22   | 00000000     | 0x0    | 22   | 00000000     | 0x0    |
> |         | 23   | 00000000     | 0x0    | 23   | 00000000     | 0x0    |
> +---------+------+--------------+--------+------+--------------+--------+
> --> here 16, 17, 18, 19 overlapping with below express buffer
> 
> +-----+-----------------------------------------------+
> |     |       SLICE 0       |        SLICE 1          |
> |     +------------+----------+------------+----------+
> |     | Start addr | End addr | Start addr | End addr |
> +-----+------------+----------+------------+----------+
> | EXP | 70024000   | 70028000 | 7002C000   | 70030000 | <-- Overlapping

Thanks for the detailed explanation with these tables.
It is very helpful. I follow both the existing and new mappings
with their help. Except for one thing.

It's not clear how EXP was set to the values on the line above.
Probably I'm missing something very obvious.
Could you help me out here?

> | PRE | 70030000   | 70033800 | 70034000   | 70037800 |
> +-----+------------+----------+------------+----------+
> 
> +---------------------+----------+----------+
> |                     | SLICE 0  |  SLICE 1 |
> +---------------------+----------+----------+
> | Default Drop Offset | 00000000 | 00000000 |     <-- Field not configured
> +---------------------+----------+----------+

...