linux-kernel - [RFC PATCH 08/10] irqchip/gic-v3-its: Use irq_chip_ack

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Date:   Thu,  8 Apr 2021 16:43:24 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>
Subject: [RFC PATCH 08/10] irqchip/gic-v3-its: Use irq_chip_ack_parent()

Subsequent patches will make the GIC irqchips use a flow handler that
issues an ->irq_ack(). irqchips of child domains need to handle this.

Note: I'm very much not fond of this; this is treacherous and explodes if
any parent chip doesn't have an ->ack() callback. It turns out okay with
EOImode=0 because handle_fasteoi_irq() doesn't issue any ->ack(), but that
is very fragile at best.

An alternative would be to
o make irq_chip_ack_parent() check the callback against NULL
o make irq_chip_ack_parent() the default chip->irq_ack() via
  MSI_FLAG_USE_DEF_CHIP_OPS.

XXX: what about pMSI and fMSI ?

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 drivers/irqchip/irq-gic-v3-its-pci-msi.c | 1 +
 drivers/irqchip/irq-gic-v3-its.c         | 1 +
 2 files changed, 2 insertions(+)

diff --git a/drivers/irqchip/irq-gic-v3-its-pci-msi.c b/drivers/irqchip/irq-gic-v3-its-pci-msi.c
index ad2810c017ed..5bc2787ee86a 100644
--- a/drivers/irqchip/irq-gic-v3-its-pci-msi.c
+++ b/drivers/irqchip/irq-gic-v3-its-pci-msi.c
@@ -27,6 +27,7 @@ static struct irq_chip its_msi_irq_chip = {
 	.name			= "ITS-MSI",
 	.irq_unmask		= its_unmask_msi_irq,
 	.irq_mask		= its_mask_msi_irq,
+	.irq_ack		= irq_chip_ack_parent,
 	.irq_eoi		= irq_chip_eoi_parent,
 	.irq_write_msi_msg	= pci_msi_domain_write_msg,
 };
diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index c3485b230d70..d6856750c084 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -1971,6 +1971,7 @@ static struct irq_chip its_irq_chip = {
 	.name			= "ITS",
 	.irq_mask		= its_mask_irq,
 	.irq_unmask		= its_unmask_irq,
+	.irq_ack		= irq_chip_ack_parent,
 	.irq_eoi		= irq_chip_eoi_parent,
 	.irq_set_affinity	= its_set_affinity,
 	.irq_compose_msi_msg	= its_irq_compose_msi_msg,
-- 
2.25.1