Change in coreboot[master]: [WIP,RFC] Clean up spinlocks

[Kyösti Mälkki (Code Review)]

Attention is currently required from: Jason Glenesk, Raul Rangel, Marshall Dawson, Tim Wawrzynczak, Julius Werner, Karthikeyan Ramasubramanian, Felix Held.
Kyösti Mälkki has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/59094 )

Change subject: [WIP,RFC] Clean up spinlocks
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Patch Set 2:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/59094/comment/98b42155_7c2d16ad 
PS2, Line 14: IMO commit a98d302fe9 x86/smp/spinlock: Disable thread coop when taking spinlock
            : is wrong and should be reverted too.
> I'm fine doing that if we can come up with another way of preventing udelay from calling `thread_yie […]

Do not hold spinlock while calling udelay(), use thread_mutex() instead to guard sections where context switching may happen.

Now I am not going to -2 these threding and spinlock changes. Just understand your DMA performance currently relies on periodic context switches, and you really really should not rely on uart8250mem and printk() to satisfy that. Or am I missing something, I did not read the DMA code that thoroughly.