Re: [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support

On Tue, Aug 25, 2020 at 11:23:56AM +0200, Kurt Kanzenbach wrote:

On Mon Aug 24 2020, Vinicius Costa Gomes wrote:

quoted

Hi,

Kurt Kanzenbach [off-list ref] writes:

[snip]

quoted

quoted

+	/* Setup timer for schedule switch: The IP core only allows to set a
+	 * cycle start timer 8 seconds in the future. This is why we setup the
+	 * hritmer to base_time - 5 seconds. Then, we have enough time to
+	 * activate IP core's EST timer.
+	 */
+	start = ktime_sub_ns(schedule->base_time, (u64)5 * NSEC_PER_SEC);
+	hrtimer_start_range_ns(&hellcreek_port->cycle_start_timer, start,
+			       NSEC_PER_SEC, HRTIMER_MODE_ABS);

If we are talking about seconds here, I don't think you need to use a
hrtimer, you could use a workqueue/delayed_work. Should make things a
bit simpler.

I've used hrtimers for one reason: The hrtimer provides a way to fire at
an absolute base time based on CLOCK_TAI. All the other facilities such
as workqueues, timer list timers, etc do not.

That still doesn't justify the complexity of irqsave spinlocks and such.
You could just as well schedule a workqueue from that hrtimer and have
process context...

Thanks,
-Vladimir