arch: Remove Itanium (IA-64) architecture

The Itanium architecture is obsolete, and an informal survey [0] reveals
that any residual use of Itanium hardware in production is mostly HP-UX
or OpenVMS based. The use of Linux on Itanium appears to be limited to
enthusiasts that occasionally boot a fresh Linux kernel to see whether
things are still working as intended, and perhaps to churn out some
distro packages that are rarely used in practice.

None of the original companies behind Itanium still produce or support
any hardware or software for the architecture, and it is listed as
'Orphaned' in the MAINTAINERS file, as apparently, none of the engineers
that contributed on behalf of those companies (nor anyone else, for that
matter) have been willing to support or maintain the architecture
upstream or even be responsible for applying the odd fix. The Intel
firmware team removed all IA-64 support from the Tianocore/EDK2
reference implementation of EFI in 2018. (Itanium is the original
architecture for which EFI was developed, and the way Linux supports it
deviates significantly from other architectures.) Some distros, such as
Debian and Gentoo, still maintain [unofficial] ia64 ports, but many have
dropped support years ago.

While the argument is being made [1] that there is a 'for the common
good' angle to being able to build and run existing projects such as the
Grid Community Toolkit [2] on Itanium for interoperability testing, the
fact remains that none of those projects are known to be deployed on
Linux/ia64, and very few people actually have access to such a system in
the first place. Even if there were ways imaginable in which Linux/ia64
could be put to good use today, what matters is whether anyone is
actually doing that, and this does not appear to be the case.

There are no emulators widely available, and so boot testing Itanium is
generally infeasible for ordinary contributors. GCC still supports IA-64
but its compile farm [3] no longer has any IA-64 machines. GLIBC would
like to get rid of IA-64 [4] too because it would permit some overdue
code cleanups. In summary, the benefits to the ecosystem of having IA-64
be part of it are mostly theoretical, whereas the maintenance overhead
of keeping it supported is real.

So let's rip off the band aid, and remove the IA-64 arch code entirely.
This follows the timeline proposed by the Debian/ia64 maintainer [5],
which removes support in a controlled manner, leaving IA-64 in a known
good state in the most recent LTS release. Other projects will follow
once the kernel support is removed.

[0] https://lore.kernel.org/all/CAMj1kXFCMh_578jniKpUtx_j8ByHnt=s7S+yQ+vGbKt9ud7+kQ@mail.gmail.com/
[1] https://lore.kernel.org/all/0075883c-7c51-00f5-2c2d-5119c1820410@web.de/
[2] https://gridcf.org/gct-docs/latest/index.html
[3] https://cfarm.tetaneutral.net/machines/list/
[4] https://lore.kernel.org/all/87bkiilpc4.fsf@mid.deneb.enyo.de/
[5] https://lore.kernel.org/all/ff58a3e76e5102c94bb5946d99187b358def688a.camel@physik.fu-berlin.de/

Acked-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

1 files changed, 0 insertions, 181 deletions

diff --git a/arch/ia64/kernel/irq.c b/arch/ia64/kernel/irq.c
deleted file mode 100644
index 275b9ea58c64..000000000000
--- a/arch/ia64/kernel/irq.c
+++ /dev/null
@@ -1,181 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- *	linux/arch/ia64/kernel/irq.c
- *
- *	Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
- *
- * This file contains the code used by various IRQ handling routines:
- * asking for different IRQs should be done through these routines
- * instead of just grabbing them. Thus setups with different IRQ numbers
- * shouldn't result in any weird surprises, and installing new handlers
- * should be easier.
- *
- * Copyright (C) Ashok Raj<ashok.raj@intel.com>, Intel Corporation 2004
- *
- * 4/14/2004: Added code to handle cpu migration and do safe irq
- *			migration without losing interrupts for iosapic
- *			architecture.
- */
-
-#include <asm/delay.h>
-#include <linux/uaccess.h>
-#include <linux/module.h>
-#include <linux/seq_file.h>
-#include <linux/interrupt.h>
-#include <linux/kernel_stat.h>
-
-#include <asm/mca.h>
-#include <asm/xtp.h>
-
-/*
- * 'what should we do if we get a hw irq event on an illegal vector'.
- * each architecture has to answer this themselves.
- */
-void ack_bad_irq(unsigned int irq)
-{
-	printk(KERN_ERR "Unexpected irq vector 0x%x on CPU %u!\n", irq, smp_processor_id());
-}
-
-/*
- * Interrupt statistics:
- */
-
-atomic_t irq_err_count;
-
-/*
- * /proc/interrupts printing:
- */
-int arch_show_interrupts(struct seq_file *p, int prec)
-{
-	seq_printf(p, "ERR: %10u\n", atomic_read(&irq_err_count));
-	return 0;
-}
-
-#ifdef CONFIG_SMP
-static char irq_redir [NR_IRQS]; // = { [0 ... NR_IRQS-1] = 1 };
-
-void set_irq_affinity_info (unsigned int irq, int hwid, int redir)
-{
-	if (irq < NR_IRQS) {
-		irq_data_update_affinity(irq_get_irq_data(irq),
-					 cpumask_of(cpu_logical_id(hwid)));
-		irq_redir[irq] = (char) (redir & 0xff);
-	}
-}
-#endif /* CONFIG_SMP */
-
-int __init arch_early_irq_init(void)
-{
-	ia64_mca_irq_init();
-	return 0;
-}
-
-#ifdef CONFIG_HOTPLUG_CPU
-unsigned int vectors_in_migration[NR_IRQS];
-
-/*
- * Since cpu_online_mask is already updated, we just need to check for
- * affinity that has zeros
- */
-static void migrate_irqs(void)
-{
-	int 		irq, new_cpu;
-
-	for (irq=0; irq < NR_IRQS; irq++) {
-		struct irq_desc *desc = irq_to_desc(irq);
-		struct irq_data *data = irq_desc_get_irq_data(desc);
-		struct irq_chip *chip = irq_data_get_irq_chip(data);
-
-		if (irqd_irq_disabled(data))
-			continue;
-
-		/*
-		 * No handling for now.
-		 * TBD: Implement a disable function so we can now
-		 * tell CPU not to respond to these local intr sources.
-		 * such as ITV,CPEI,MCA etc.
-		 */
-		if (irqd_is_per_cpu(data))
-			continue;
-
-		if (cpumask_any_and(irq_data_get_affinity_mask(data),
-				    cpu_online_mask) >= nr_cpu_ids) {
-			/*
-			 * Save it for phase 2 processing
-			 */
-			vectors_in_migration[irq] = irq;
-
-			new_cpu = cpumask_any(cpu_online_mask);
-
-			/*
-			 * Al three are essential, currently WARN_ON.. maybe panic?
-			 */
-			if (chip && chip->irq_disable &&
-				chip->irq_enable && chip->irq_set_affinity) {
-				chip->irq_disable(data);
-				chip->irq_set_affinity(data,
-						       cpumask_of(new_cpu), false);
-				chip->irq_enable(data);
-			} else {
-				WARN_ON((!chip || !chip->irq_disable ||
-					 !chip->irq_enable ||
-					 !chip->irq_set_affinity));
-			}
-		}
-	}
-}
-
-void fixup_irqs(void)
-{
-	unsigned int irq;
-	extern void ia64_process_pending_intr(void);
-	extern volatile int time_keeper_id;
-
-	/* Mask ITV to disable timer */
-	ia64_set_itv(1 << 16);
-
-	/*
-	 * Find a new timesync master
-	 */
-	if (smp_processor_id() == time_keeper_id) {
-		time_keeper_id = cpumask_first(cpu_online_mask);
-		printk ("CPU %d is now promoted to time-keeper master\n", time_keeper_id);
-	}
-
-	/*
-	 * Phase 1: Locate IRQs bound to this cpu and
-	 * relocate them for cpu removal.
-	 */
-	migrate_irqs();
-
-	/*
-	 * Phase 2: Perform interrupt processing for all entries reported in
-	 * local APIC.
-	 */
-	ia64_process_pending_intr();
-
-	/*
-	 * Phase 3: Now handle any interrupts not captured in local APIC.
-	 * This is to account for cases that device interrupted during the time the
-	 * rte was being disabled and re-programmed.
-	 */
-	for (irq=0; irq < NR_IRQS; irq++) {
-		if (vectors_in_migration[irq]) {
-			struct pt_regs *old_regs = set_irq_regs(NULL);
-
-			vectors_in_migration[irq]=0;
-			generic_handle_irq(irq);
-			set_irq_regs(old_regs);
-		}
-	}
-
-	/*
-	 * Now let processor die. We do irq disable and max_xtp() to
-	 * ensure there is no more interrupts routed to this processor.
-	 * But the local timer interrupt can have 1 pending which we
-	 * take care in timer_interrupt().
-	 */
-	max_xtp();
-	local_irq_disable();
-}
-#endif