linux-kernel - [RFC PATCH v2 2/5] irqchip/realtek-rtl: fix off-by-one in routing

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Date:   Sun, 26 Dec 2021 20:59:25 +0100
From:   Sander Vanheule <sander@...nheule.net>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Cc:     Birger Koblitz <mail@...ger-koblitz.de>,
        Bert Vermeulen <bert@...t.com>,
        John Crispin <john@...ozen.org>, linux-kernel@...r.kernel.org,
        Sander Vanheule <sander@...nheule.net>
Subject: [RFC PATCH v2 2/5] irqchip/realtek-rtl: fix off-by-one in routing

There is an offset between routing values (1..6) and the connected MIPS
CPU interrupts (2..7), but no distinction was made between these two
values.

This issue was previously hidden during testing, because an interrupt
mapping was used where for each required interrupt another (unused)
routing was configured, with an offset of +1.

Offset the CPU IRQ numbers by -1 to retrieve the correct routing value.

Fixes: 9f3a0f34b84a ("irqchip: Add support for Realtek RTL838x/RTL839x interrupt controller")
Signed-off-by: Sander Vanheule <sander@...nheule.net>
---
 drivers/irqchip/irq-realtek-rtl.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/irq-realtek-rtl.c b/drivers/irqchip/irq-realtek-rtl.c
index d6788dd93c7b..568614edd88f 100644
--- a/drivers/irqchip/irq-realtek-rtl.c
+++ b/drivers/irqchip/irq-realtek-rtl.c
@@ -95,7 +95,8 @@ static void realtek_irq_dispatch(struct irq_desc *desc)
  * SoC interrupts are cascaded to MIPS CPU interrupts according to the
  * interrupt-map in the device tree. Each SoC interrupt gets 4 bits for
  * the CPU interrupt in an Interrupt Routing Register. Max 32 SoC interrupts
- * thus go into 4 IRRs.
+ * thus go into 4 IRRs. A routing value of '0' means the interrupt is left
+ * disconnected. Routing values {1..15} connect to output lines {0..14}.
  */
 static int __init map_interrupts(struct device_node *node, struct irq_domain *domain)
 {
@@ -134,7 +135,7 @@ static int __init map_interrupts(struct device_node *node, struct irq_domain *do
 		of_node_put(cpu_ictl);
 
 		cpu_int = be32_to_cpup(imap + 2);
-		if (cpu_int > 7)
+		if (cpu_int > 7 || cpu_int < 2)
 			return -EINVAL;
 
 		if (!(mips_irqs_set & BIT(cpu_int))) {
@@ -143,7 +144,8 @@ static int __init map_interrupts(struct device_node *node, struct irq_domain *do
 			mips_irqs_set |= BIT(cpu_int);
 		}
 
-		regs[(soc_int * 4) / 32] |= cpu_int << (soc_int * 4) % 32;
+		/* Use routing values (1..6) for CPU interrupts (2..7) */
+		regs[(soc_int * 4) / 32] |= (cpu_int - 1) << (soc_int * 4) % 32;
 		imap += 3;
 	}
 
-- 
2.33.1