Re: [PATCH 2/2] ARM: tegra: Use DT /cpu node to detect number of CPU core

On Mon, Jan 14, 2013 at 09:49:25AM +0000, Hiroshi Doyu wrote:

Hi Russell,

Russell King - ARM Linux [off-list ref] wrote @ Mon, 14 Jan 2013 10:27:20 +0100:

quoted

On Mon, Jan 14, 2013 at 09:52:50AM +0200, Hiroshi Doyu wrote:

quoted

+	if (!arm_dt_cpu_map_valid())
+		set_cpu_possible(0, true);

You don't need to do any of this (and, therefore, I don't think you even
need the first patch.)

The generic boot code will set CPU0 as possible, present and online.  Think
about it: you're booting on that very CPU so it better be possible, present
and online.  If it isn't, what CPU is executing your code?

arm_dt_init_cpu_maps() will only ever set _additional_ CPUs in the possible
map.

Ergo, by the time the above code is run, CPU0 will already be marked as
possible.  Therefore, the above code and arm_dt_cpu_map_valid() is not
required.

Right.

In Tegra, we've decided to not use SCU based detection at all any more
and to continue with a single core even when DT cpu detection
fails. For Tegra, "arm_dt_cpu_map_valid()" is not necessary. For other
SoCs, this would be necessary when they want to detect again with
SCU.

Correct. I will keep my patch around and repost it if and when we want other
platforms to rely on legacy HW number of cores count discovery.

Given that's going to be temporary legacy code anyway, I hope we won't need it
at all.

Lorenzo