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().

Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
---
 kernel/irq/irqdesc.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 21a968bc468b..a4911f7ebb07 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -556,27 +556,24 @@ int __init early_irq_init(void)
 
 #else /* !CONFIG_SPARSE_IRQ */
 
-struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
-	[0 ... NR_IRQS-1] = {
-		.handle_irq	= handle_bad_irq,
-		.depth		= 1,
-		.lock		= __RAW_SPIN_LOCK_UNLOCKED(irq_desc->lock),
-	}
-};
+static struct irq_desc *irq_descs;
 
 int __init early_irq_init(void)
 {
-	int count, i, node = first_online_node;
+	int i, node = first_online_node;
 	struct irq_desc *desc;
 
 	init_irq_default_affinity();
 
 	printk(KERN_INFO "NR_IRQS: %d\n", NR_IRQS);
 
-	desc = irq_desc;
-	count = ARRAY_SIZE(irq_desc);
+	desc = kmalloc_array(NR_IRQS, sizeof(*desc), GFP_KERNEL | __GFP_ZERO);
+	if (desc == NULL)
+		return -ENOMEM;
+
+	irq_descs = desc;
 
-	for (i = 0; i < count; i++) {
+	for (i = 0; i < NR_IRQS; i++) {
 		desc[i].kstat_irqs = alloc_percpu(unsigned int);
 		alloc_masks(&desc[i], node);
 		raw_spin_lock_init(&desc[i].lock);
@@ -593,7 +590,7 @@ int __init early_irq_init(void)
 
 struct irq_desc *irq_to_desc(unsigned int irq)
 {
-	return (irq < NR_IRQS) ? irq_desc + irq : NULL;
+	return (irq < NR_IRQS) ? irq_descs + irq : NULL;
 }
 EXPORT_SYMBOL(irq_to_desc);
 
-- 
2.25.1

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.

That allocation does not buy us much.

Thanks,

        tglx

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

On Tue, Jan 31 2023 at 10:41, Shanker Donthineni wrote:
> On 1/31/23 03:16, Thomas Gleixner wrote:
>> 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.

This needs some thought.

> Can work on this after moving it to maple tree?

Yup. Just drop this patch.

Thanks,

        tglx