On Mon, 19 Jul 2021 14:07:33 -0400, Nitesh Narayan Lal wrote:

From: Thomas Gleixner <redacted>

The discussion about removing the side effect of irq_set_affinity_hint() of
actually applying the cpumask (if not NULL) as affinity to the interrupt,
unearthed a few unpleasantries:

  1) The modular perf drivers rely on the current behaviour for the very
     wrong reasons.

  2) While none of the other drivers prevents user space from changing
     the affinity, a cursorily inspection shows that there are at least
     expectations in some drivers.

#1 needs to be cleaned up anyway, so that's not a problem

#2 might result in subtle regressions especially when irqbalanced (which
   nowadays ignores the affinity hint) is disabled.

Provide new interfaces:

  irq_update_affinity_hint()  - Only sets the affinity hint pointer
  irq_set_affinity_and_hint() - Set the pointer and apply the affinity to
                                the interrupt

Make irq_set_affinity_hint() a wrapper around irq_apply_affinity_hint() and
document it to be phased out.

Signed-off-by: Thomas Gleixner <redacted>
Signed-off-by: Nitesh Narayan Lal <redacted>
Link: https://lore.kernel.org/r/20210501021832.743094-1-jesse.brandeburg@intel.com (local)

include/linux/interrupt.h:343: warning: Function parameter or member 'm' not described in 'irq_update_affinity_hint'
include/linux/interrupt.h:343: warning: Excess function parameter 'cpumask' description in 'irq_update_affinity_hint'
include/linux/interrupt.h:358: warning: Function parameter or member 'm' not described in 'irq_set_affinity_and_hint'
include/linux/interrupt.h:358: warning: Excess function parameter 'cpumask' description in 'irq_set_affinity_and_hint'