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sfc: document TC-to-EF100-MAE action translation concepts

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Includes an explanation of the lifetime of the 'cursor' action-set `act`.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Edward Cree 2023-03-27 11:36:03 +01:00 committed by David S. Miller
parent 37018b5a29
commit edd025ca08
1 changed files with 25 additions and 1 deletions
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26
drivers/net/ethernet/sfc/tc.c
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@ -66,7 +66,7 @@ static const struct rhashtable_params efx_tc_match_action_ht_params = {
static void efx_tc_free_action_set(struct efx_nic *efx,
struct efx_tc_action_set *act, bool in_hw)
{
/* Failure paths calling this on the 'running action' set in_hw=false,
/* Failure paths calling this on the 'cursor' action set in_hw=false,
* because if the alloc had succeeded we'd've put it in acts.list and
* not still have it in act.
*/
@ -407,6 +407,30 @@ static int efx_tc_flower_replace(struct efx_nic *efx,
goto release;
}
/**
* DOC: TC action translation
*
* Actions in TC are sequential and cumulative, with delivery actions
* potentially anywhere in the order. The EF100 MAE, however, takes
* an 'action set list' consisting of 'action sets', each of which is
* applied to the _original_ packet, and consists of a set of optional
* actions in a fixed order with delivery at the end.
* To translate between these two models, we maintain a 'cursor', @act,
* which describes the cumulative effect of all the packet-mutating
* actions encountered so far; on handling a delivery (mirred or drop)
* action, once the action-set has been inserted into hardware, we
* append @act to the action-set list (@rule->acts); if this is a pipe
* action (mirred mirror) we then allocate a new @act with a copy of
* the cursor state _before_ the delivery action, otherwise we set @act
* to %NULL.
* This ensures that every allocated action-set is either attached to
* @rule->acts or pointed to by @act (and never both), and that only
* those action-sets in @rule->acts exist in hardware. Consequently,
* in the failure path, @act only needs to be freed in memory, whereas
* for @rule->acts we remove each action-set from hardware before
* freeing it (efx_tc_free_action_set_list()), even if the action-set
* list itself is not in hardware.
*/
flow_action_for_each(i, fa, &fr->action) {
struct efx_tc_action_set save;
u16 tci;