Re: [PATCH V3 4/4] clocksource: mips-gic: Add device-tree support

Hi Mark,

quoted

+static void __init gic_clocksource_of_init(struct device_node *node)
+{
+     if (of_property_read_u32(node, "clock-frequency", &gic_frequency)) {
+             pr_err("GIC frequency not specified.\n");
+             return;
+     }
+     gic_timer_irq = irq_of_parse_and_map(node, 0);
+     if (!gic_timer_irq) {
+             pr_err("GIC timer IRQ not specified.\n");
+             return;
+     }
+
+     __gic_clocksource_init();
+}
+CLOCKSOURCE_OF_DECLARE(mips_gic_timer, "mti,interaptiv-gic-timer",
+                    gic_clocksource_of_init);

Your binding document expected the timer node under the GIC node, and it
looks like this relies on GIC internals. Hwoever, this allows for people
to put the timer node anywhere (and it turns out people are _really_ bad
at putting things together as the binding author expected).

It might be better if the GIC driver detected the sub node and probed
the clocksource driver (or registered a platform device that the
clocksource driver gets registered from). that could prevent some
horrible issues with probe ordering and/or bad dts.

Probing the clocksource during probe of the irqchip doesn't work
because time-keeping isn't set up at the time.  Registering a platform
device for the timer pushes back GIC timer registration to later in
the boot process (assuming it now becomes a module_platform_driver)
and makes it rather non-parallel to how it's done in the non-DT case
(this could be changed, though IMO it's a lot of churn just to thwart
bad DT authors).

Probe ordering shouldn't be an issue because irqchips are probed
before clocksources.  Perhaps checking for the presence of GIC
(there's the global gic_present) and node->parent (to enforce the
parent-child relationship) would be sufficient?

Thanks,
Andrew
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