linux-kernel - Affinity setting problem for emulated MSI on PLIC

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Message-ID: <20250722224513.22125-1-inochiama@gmail.com>
Date: Wed, 23 Jul 2025 06:45:11 +0800
From: Inochi Amaoto <inochiama@...il.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	Chen Wang <unicorn_wang@...look.com>
Cc: Inochi Amaoto <inochiama@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Affinity setting problem for emulated MSI on PLIC

SG2044 and SG2042 has a msi controller that converts the PLIC interrupt
to a MSI one. It works at the most case, but failed when probing NVME.
The driver complains "nvme nvme0: I/O tag XXX (XXX) QID XX timeout,
completion polled". After some test, I found this is caused by some
broken interrupt, which is disable on the underlying PLIC chip after
setting affinity. As the MSI chip does not have a enable function,
irq_startup only calls irq_unmask. This make the underlying interrupt
at PLIC is not enabled.

I have done a hack by changing the mask/unmask to disable/enable and
setting MSI_FLAG_PCI_MSI_MASK_PARENT to solve this and it works.
But I wonder whether there is something better to solve this problem?
(The hack I have done is at the end of mail)

Regards,
Inochi

diff --git a/drivers/irqchip/irq-sg2042-msi.c b/drivers/irqchip/irq-sg2042-msi.c
index bcfddc51bc6a..ea5bf6fb6711 100644
--- a/drivers/irqchip/irq-sg2042-msi.c
+++ b/drivers/irqchip/irq-sg2042-msi.c
@@ -94,6 +94,20 @@ static const struct irq_chip sg2042_msi_middle_irq_chip = {
 	.irq_compose_msi_msg	= sg2042_msi_irq_compose_msi_msg,
 };

+/*
+ * As PLIC can only apply affinity when enabling, so always call enable
+ * when unmasking interrupt.
+ */
+static void sg2044_msi_irq_mask(struct irq_data *d)
+{
+	irq_chip_disable_parent(d);
+}
+
+static void sg2044_msi_irq_unmask(struct irq_data *d)
+{
+	irq_chip_enable_parent(d);
+}
+
 static void sg2044_msi_irq_ack(struct irq_data *d)
 {
 	struct sg204x_msi_chipdata *data = irq_data_get_irq_chip_data(d);
@@ -115,8 +129,8 @@ static void sg2044_msi_irq_compose_msi_msg(struct irq_data *d, struct msi_msg *m
 static struct irq_chip sg2044_msi_middle_irq_chip = {
 	.name			= "SG2044 MSI",
 	.irq_ack		= sg2044_msi_irq_ack,
-	.irq_mask		= irq_chip_mask_parent,
-	.irq_unmask		= irq_chip_unmask_parent,
+	.irq_mask		= sg2044_msi_irq_mask,
+	.irq_unmask		= sg2044_msi_irq_unmask,
 #ifdef CONFIG_SMP
 	.irq_set_affinity	= irq_chip_set_affinity_parent,
 #endif
@@ -201,7 +215,8 @@ static const struct msi_parent_ops sg2042_msi_parent_ops = {
 };

 #define SG2044_MSI_FLAGS_REQUIRED (MSI_FLAG_USE_DEF_DOM_OPS |	\
-				   MSI_FLAG_USE_DEF_CHIP_OPS)
+				   MSI_FLAG_USE_DEF_CHIP_OPS |	\
+				   MSI_FLAG_PCI_MSI_MASK_PARENT)

 #define SG2044_MSI_FLAGS_SUPPORTED (MSI_GENERIC_FLAGS_MASK |	\
 				    MSI_FLAG_PCI_MSIX)
--
2.50.1