asm-generic: New generic ticket-based spinlock
This contains a new ticket-based spinlock that uses only generic
atomics and doesn't require as much from the memory system as qspinlock
does in order to be fair. It also includes a bit of documentation about
the qspinlock and qrwlock fairness requirements.
This will soon be used by a handful of architectures that don't meet the
qspinlock requirements.
* tag 'generic-ticket-spinlocks-v6':
csky: Move to generic ticket-spinlock
RISC-V: Move to queued RW locks
RISC-V: Move to generic spinlocks
openrisc: Move to ticket-spinlock
asm-generic: qrwlock: Document the spinlock fairness requirements
asm-generic: qspinlock: Indicate the use of mixed-size atomics
asm-generic: ticket-lock: New generic ticket-based spinlock
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