[RFC PATCH 0/6] Unify the Interrupt Mode and setup it as soon as possible

[Dou Liyang]

According to Ingo's and Eric's advice[1,2], Try my best to optimize the 
init of Interrupt Mode for x86.

The MP specification defines three different interrupt modes as follows:

 1. PIC Mode
 2. Virtual Wire Mode
 3. Symmetic I/O Mode

Currently, In kernel,

1. Setup the Virtual Wire Mode during the IRQ initialization(
step 1 in the following figure).
2. Enable and Setup the Symmetic I/O Mode either during the
SMP-capabe system prepares CPUs(step 2) or during the UP system 
initializes itself(step 3).

  start_kernel
+---------------+
|
+--> .......
|
|    setup_arch
+--> +-------+
|
|    init_IRQ
+-> +--+-----+
|      |        init_ISA_irqs
|      +------> +-+--------+
|                 |         +----------------+
+--->             +------>  | 1.init_bsp_APIC|
|     .......               +----------------+
+--->
|     rest_init
+--->---+-----+
|       |   kernel_init
|       +> ----+-----+
|              |   kernel_init_freeable
|              +->  ----+-------------+
|                       |     smp_prepare_cpus
|                       +---> +----+---------+
|                       |          |   +-------------------+
|                       |          +-> |2.  apic_bsp_setup |
|                       |              +-------------------+
|                       |
v                       |     smp_init
                        +---> +---+----+
                                  |    +-------------------+
                                  +--> |3.  apic_bsp_setup |
                                       +-------------------+

The purpose of this patchset is Unifing these setup steps and executing as
soon as possible as follows:

   start_kernel
---------------+
|
|
|
|     init_IRQ
+---->---+----+
|        |
|        |      +--------------------+
|        +----> | 4. init_bsp_APIC   |
|               +--------------------+
v

By the way, Also fix a bug about kexec[3].


Some doubts, need help:

1. Patchset has influence on IOMMU in enable_IR_x2apic(). Not sure
it can be in advance?

2. Due to 

Commit 8c3ba8d04924 ("x86, apic: ack all pending irqs when crashed/on kexec")

 ..., patchset also needs TSC and uses the "cpu_khz" in setup_local_APIC().
And a warning[4] will be triggered when crashed/on kexec. Not sure how to
modify?

[1]. https://lkml.org/lkml/2016/8/2/929
[2]. https://lkml.org/lkml/2016/8/1/506
[3]. https://lkml.org/lkml/2016/7/25/1118
[4]. WARN_ON(max_loops <= 0) in setup_local_APIC()

Dou Liyang (6):
  x86/apic: Replace init_bsp_APIC() with apic_virture_wire_mode_setup()
  x86/apic: Construct a framework for setuping APIC mode as soon as
    possible
  x86/apic: Extract APIC timer related code from apic_bsp_setup()
  x86/apic: Make the APIC mode setup earlier for SMP-capable system
  x86/apic: Make the APIC mode setup earlier for UP system
  x86/apic: Remove the apic_virture_wire_mode_setup()

 arch/x86/include/asm/apic.h    |   7 +-
 arch/x86/include/asm/io_apic.h |   2 +
 arch/x86/kernel/apic/apic.c    | 218 ++++++++++++++++++++++++-----------------
 arch/x86/kernel/apic/io_apic.c |   4 +-
 arch/x86/kernel/irqinit.c      |   6 +-
 arch/x86/kernel/smpboot.c      |  68 ++-----------
 6 files changed, 149 insertions(+), 156 deletions(-)

-- 
2.5.5