irqchip/sifive-plic: Avoid interrupt ID 0 handling during suspend/resume

[ Upstream commit f75e07bf5226da640fa99a0594687c780d9bace4 ]

According to the PLIC specification[1], global interrupt sources are
assigned small unsigned integer identifiers beginning at the value 1.
An interrupt ID of 0 is reserved to mean "no interrupt".

The current plic_irq_resume() and plic_irq_suspend() functions incorrectly
start the loop from index 0, which accesses the register space for the
reserved interrupt ID 0.

Change the loop to start from index 1, skipping the reserved
interrupt ID 0 as per the PLIC specification.

This prevents potential undefined behavior when accessing the reserved
register space during suspend/resume cycles.

Fixes: e80f0b6a2cf3 ("irqchip/irq-sifive-plic: Add syscore callbacks for hibernation")
Co-developed-by: Jia Wang <wangjia@ultrarisc.com>
Signed-off-by: Jia Wang <wangjia@ultrarisc.com>
Co-developed-by: Charles Mirabile <cmirabil@redhat.com>
Signed-off-by: Charles Mirabile <cmirabil@redhat.com>
Signed-off-by: Lucas Zampieri <lzampier@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://github.com/riscv/riscv-plic-spec/releases/tag/1.0.0
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index bf69a4802b71e7875b2a7c96ccaa0e0b3c7e9e70..9c4af7d58846318a66eb29c2fd9000f04603a7ca 100644 (file)
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -252,7 +252,8 @@ static int plic_irq_suspend(void)
 
        priv = per_cpu_ptr(&plic_handlers, smp_processor_id())->priv;
 
-       for (i = 0; i < priv->nr_irqs; i++) {
+       /* irq ID 0 is reserved */
+       for (i = 1; i < priv->nr_irqs; i++) {
                __assign_bit(i, priv->prio_save,
                             readl(priv->regs + PRIORITY_BASE + i * PRIORITY_PER_ID));
        }
@@ -283,7 +284,8 @@ static void plic_irq_resume(void)
 
        priv = per_cpu_ptr(&plic_handlers, smp_processor_id())->priv;
 
-       for (i = 0; i < priv->nr_irqs; i++) {
+       /* irq ID 0 is reserved */
+       for (i = 1; i < priv->nr_irqs; i++) {
                index = BIT_WORD(i);
                writel((priv->prio_save[index] & BIT_MASK(i)) ? 1 : 0,
                       priv->regs + PRIORITY_BASE + i * PRIORITY_PER_ID);