linux-kernel - Re: [PATCH 2/5] genirq: Allocate IRQ descriptors at boot time for !SPARSEIRQ

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Date:   Tue, 31 Jan 2023 10:41:25 -0600
From:   Shanker Donthineni <sdonthineni@...dia.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>, Michael Walle <michael@...le.cc>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Hans de Goede <hdegoede@...hat.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] genirq: Allocate IRQ descriptors at boot time for
 !SPARSEIRQ



On 1/31/23 03:16, Thomas Gleixner wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Sun, Jan 29 2023 at 18:57, Shanker Donthineni wrote:
> 
>> Remove the use of statically allocated arrays for IRQ descriptors.
>> Instead, allocate the necessary NR_IRQ descriptors during the boot
>> time in early_irq_init().
> 
> That's not what I meant. I was pondering to remove !SPARSEIRQ
> completely.
> 

It's touching many files to drop CONFIG_SPARSE_IRQ=n support. Worried
about removing !SPARSEIRQ without testing on legacy platforms.

Can work on this after moving it to maple tree?

  arch/arm/Kconfig           |  1 -
  arch/arm/include/asm/irq.h |  4 --
  arch/arm/kernel/irq.c      |  2 -
  arch/arm64/Kconfig         |  1 -
  arch/csky/Kconfig          |  1 -
  arch/loongarch/Kconfig     |  1 -
  arch/microblaze/Kconfig    |  1 -
  arch/nios2/Kconfig         |  1 -
  arch/openrisc/Kconfig      |  1 -
  arch/powerpc/Kconfig       |  1 -
  arch/riscv/Kconfig         |  1 -
  arch/s390/Kconfig          |  1 -
  arch/sh/Kconfig            |  1 -
  arch/sparc/Kconfig         |  1 -
  arch/x86/Kconfig           |  1 -
  drivers/irqchip/Kconfig    |  5 ---
  include/linux/irqdesc.h    |  8 ----
  kernel/irq/Kconfig         | 17 --------
  kernel/irq/chip.c          |  5 ---
  kernel/irq/internals.h     | 10 -----
  kernel/irq/irqdesc.c       | 88 --------------------------------------
  kernel/irq/irqdomain.c     | 14 +++---
  22 files changed, 6 insertions(+), 160 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 43c7773b89ae..d4fc6c549660 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -134,7 +134,6 @@ config ARM
         select PCI_SYSCALL if PCI
         select PERF_USE_VMALLOC
         select RTC_LIB
-       select SPARSE_IRQ if !(ARCH_FOOTBRIDGE || ARCH_RPC)
         select SYS_SUPPORTS_APM_EMULATION
         select THREAD_INFO_IN_TASK
         select TIMER_OF if OF
diff --git a/arch/arm/include/asm/irq.h b/arch/arm/include/asm/irq.h
index a7c2337b0c7d..6d4ff82c40cf 100644
--- a/arch/arm/include/asm/irq.h
+++ b/arch/arm/include/asm/irq.h
@@ -4,11 +4,7 @@

...

-#ifndef CONFIG_SPARSE_IRQ
-#include <mach/irqs.h>
-#else
  #define NR_IRQS NR_IRQS_LEGACY
-#endif

...
# Make sparse irq Kconfig switch below available
-config MAY_HAVE_SPARSE_IRQ
-       bool
-
  # Legacy support, required for itanic
  config GENERIC_IRQ_LEGACY
         bool
@@ -107,19 +103,6 @@ config GENERIC_IRQ_RESERVATION_MODE
  config IRQ_FORCED_THREADING
         bool


> That allocation does not buy us much.
> 

Agree, not much value other than reducing kernel binary size. I will drop
this patch in v2.

Thanks,
Shanker