Change in coreboot[master]: arch/x86/smp/spinlock: Fix threading when !STAGE_HAS_SPINLOCKS

[Raul Rangel (Code Review)]

Attention is currently required from: Julius Werner, Kyösti Mälkki, Rob Barnes, Karthik Ramasubramanian.
Raul Rangel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/59021 )

Change subject: arch/x86/smp/spinlock: Fix threading when !STAGE_HAS_SPINLOCKS
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Patch Set 2:

(2 comments)

File src/arch/x86/include/arch/smp/spinlock.h:

https://review.coreboot.org/c/coreboot/+/59021/comment/97024a61_d124ca3a 
PS2, Line 21: 	static spinlock_t x = SPIN_LOCK_UNLOCKED;
> STAGE_HAS_DATA_SECTION could be used as guard, .data is needed. […]

The lock variable is never accessed, so the compiler just removes it. Thus we don't need a .data section.

https://review.coreboot.org/c/coreboot/+/59021/comment/28d9d0eb_6e21d4ee 
PS2, Line 50: 	thread_coop_disable();
> For a sequence like below, thread_coop_disable() is not desired? I think our spin_lock() does more t […]

In your first example, there is nothing wrong with disabling threading. There is no yield so it's really a noop. The only cost we pay is incrementing and decrementing a counter. I don't think we gain anything by adding additional API calls.