[Intel-wired-lan] [PATCH] igc: fix the validation logic for taprio's gate list

[Kurt Kanzenbach]

On Tue Mar 07 2023, AKASHI Takahiro wrote:
> The check introduced in the commit a5fd39464a40 ("igc: Lift TAPRIO schedule
> restriction") can detect a false positive error in some corner case.
> For instance,
>     tc qdisc replace ... taprio num_tc 4
> 	...
> 	sched-entry S 0x01 100000	# slot#1
> 	sched-entry S 0x03 100000	# slot#2
> 	sched-entry S 0x04 100000	# slot#3
> 	sched-entry S 0x08 200000	# slot#4
> 	flags 0x02			# hardware offload
>
> Here the queue#0 (the first queue) is on at the slot#1 and #2,
> and off at the slot#3 and #4. Under the current logic, when the slot#4
> is examined, validate_schedule() returns *false* since the enablement
> count for the queue#0 is two and it is already off at the previous slot
> (i.e. #3). But this definition is truely correct.
>
> Let's fix the logic to enforce a strict validation for consecutively-opened
> slots.
>
> Fixes: a5fd39464a40 ("igc: Lift TAPRIO schedule restriction")
> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>

Grml. Thanks!

Reviewed-by: Kurt Kanzenbach <kurt at linutronix.de>
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