[v4] genirq/msi: Add the address and data that show MSI/MSIX

[Hans Zhang]

The debug_show() callback function is implemented in the MSI core code.
And assign it to the domain ops::debug_show() creation.

When debugging MSI-related hardware issues (e.g., interrupt delivery
failures), developers currently need to either:
1. Recompile kernel with dynamic debug for tracing msi_desc.
2. Manually read device registers through low-level tools.

Both approaches become challenging in production environments where
dynamic debugging is often disabled.

This patch proposes to expose MSI address_hi/address_lo and msg_data in
`/sys/kernel/debug/irq/irqs/<msi_irq_num>`. These fields are critical to:
- Verify if MSI configuration matches hardware programming
- Diagnose interrupt routing errors (e.g., mismatched destination ID)
- Validate remapping behavior in virtualized environments

The information is already maintained in msi_desc and irq_data structures.
By surfacing it through debugfs:
- We create a unified place for runtime IRQ diagnostics
- Enable debugging without kernel rebuilds or special tools
- Align with existing exposure of IRQ chip/type/affinity data

Sample output:
  address_hi: 0x00000000
  address_lo: 0xfe670040
  msg_data:   0x00000001

Signed-off-by: Hans Zhang <18255117159@xxxxxxx>
---
Changes since v2-v3:
https://lore.kernel.org/linux-pci/20250301123953.291675-1-18255117159@xxxxxxx/
https://lore.kernel.org/linux-pci/20250302020328.296523-1-18255117159@xxxxxxx/

- Fix implicit declaration of function 'seq_printf'.
- Fix 'const struct irq_domain_ops' has no member named 'debug_show'.
- The patch commit message were modified.
- Removes the display that is not currently an MSI/MSIX interrupt.

Changes since v1:
https://lore.kernel.org/linux-pci/20250227162821.253020-1-18255117159@xxxxxxx/

- According to Thomas(tglx), the debug_show() callback should be added
  to the MSI core code.
---
 kernel/irq/msi.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index 396a067a8a56..adcc7c638295 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -15,6 +15,7 @@
 #include <linux/mutex.h>
 #include <linux/pci.h>
 #include <linux/slab.h>
+#include <linux/seq_file.h>
 #include <linux/sysfs.h>
 #include <linux/types.h>
 #include <linux/xarray.h>
@@ -756,12 +757,30 @@ static int msi_domain_translate(struct irq_domain *domain, struct irq_fwspec *fw
 	return info->ops->msi_translate(domain, fwspec, hwirq, type);
 }
 
+#ifdef CONFIG_GENERIC_IRQ_DEBUGFS
+static void msi_domain_debug_show(struct seq_file *m, struct irq_domain *d,
+				  struct irq_data *irqd, int ind)
+{
+	struct msi_desc *desc = irq_get_msi_desc(irqd->irq);
+
+	if (!desc)
+		return;
+
+	seq_printf(m, "\n%*saddress_hi: 0x%08x", ind + 1, "", desc->msg.address_hi);
+	seq_printf(m, "\n%*saddress_lo: 0x%08x", ind + 1, "", desc->msg.address_lo);
+	seq_printf(m, "\n%*smsg_data:   0x%08x\n", ind + 1, "", desc->msg.data);
+}
+#endif
+
 static const struct irq_domain_ops msi_domain_ops = {
 	.alloc		= msi_domain_alloc,
 	.free		= msi_domain_free,
 	.activate	= msi_domain_activate,
 	.deactivate	= msi_domain_deactivate,
 	.translate	= msi_domain_translate,
+#ifdef CONFIG_GENERIC_IRQ_DEBUGFS
+	.debug_show     = msi_domain_debug_show,
+#endif
 };
 
 static irq_hw_number_t msi_domain_ops_get_hwirq(struct msi_domain_info *info,

base-commit: 76544811c850a1f4c055aa182b513b7a843868ea
-- 
2.25.1