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Subject[PATCH v2 1/9] genirq/msi: Allow level-triggered MSIs to be exposed by MSI providers
Date
So far, MSIs have been used to signal edge-triggered interrupts, as
a write is a good model for an edge (you can't "unwrite" something).
On the other hand, routing zillions of wires in an SoC because you
need level interrupts is a bit extreme.

People have come up with a variety of schemes to support this, which
involves sending two messages: one to signal the interrupt, and one
to clear it. Since the kernel cannot represent this, we've ended up
with side-band mechanisms that are pretty awful.

Instead, let's acknoledge the requirement, and ensure that, under the
right circumstances, the irq_compose_msg and irq_write_msg can take
as a parameter an array of two messages instead of a pointer to a
single one. We also add some checking that the compose method only
clobbers the second message if the MSI domain has been created with
the MSI_FLAG_LEVEL_CAPABLE flags.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
include/linux/msi.h | 2 ++
kernel/irq/msi.c | 33 ++++++++++++++++++++++++---------
2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/include/linux/msi.h b/include/linux/msi.h
index 1f1bbb5b4679..5839d8062dfc 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -289,6 +289,8 @@ enum {
* MSI_FLAG_ACTIVATE_EARLY has been set.
*/
MSI_FLAG_MUST_REACTIVATE = (1 << 5),
+ /* Is level-triggered capable, using two messages */
+ MSI_FLAG_LEVEL_CAPABLE = (1 << 6),
};

int msi_domain_set_affinity(struct irq_data *data, const struct cpumask *mask,
diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index 2a8571f72b17..4ca2fd46645d 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -76,6 +76,19 @@ static inline void irq_chip_write_msi_msg(struct irq_data *data,
data->chip->irq_write_msi_msg(data, msg);
}

+static void msi_check_level(struct irq_domain *domain, struct msi_msg *msg)
+{
+ struct msi_domain_info *info = domain->host_data;
+
+ /*
+ * If the MSI provider has messed with the second message and
+ * not advertized that it is level-capable, signal the breakage.
+ */
+ WARN_ON(!((info->flags & MSI_FLAG_LEVEL_CAPABLE) &&
+ (info->chip->flags & IRQCHIP_SUPPORTS_LEVEL_MSI)) &&
+ (msg[1].address_lo || msg[1].address_hi || msg[1].data));
+}
+
/**
* msi_domain_set_affinity - Generic affinity setter function for MSI domains
* @irq_data: The irq data associated to the interrupt
@@ -89,13 +102,14 @@ int msi_domain_set_affinity(struct irq_data *irq_data,
const struct cpumask *mask, bool force)
{
struct irq_data *parent = irq_data->parent_data;
- struct msi_msg msg;
+ struct msi_msg msg[2] = { [1] = { }, };
int ret;

ret = parent->chip->irq_set_affinity(parent, mask, force);
if (ret >= 0 && ret != IRQ_SET_MASK_OK_DONE) {
- BUG_ON(irq_chip_compose_msi_msg(irq_data, &msg));
- irq_chip_write_msi_msg(irq_data, &msg);
+ BUG_ON(irq_chip_compose_msi_msg(irq_data, msg));
+ msi_check_level(irq_data->domain, msg);
+ irq_chip_write_msi_msg(irq_data, msg);
}

return ret;
@@ -104,20 +118,21 @@ int msi_domain_set_affinity(struct irq_data *irq_data,
static int msi_domain_activate(struct irq_domain *domain,
struct irq_data *irq_data, bool early)
{
- struct msi_msg msg;
+ struct msi_msg msg[2] = { [1] = { }, };

- BUG_ON(irq_chip_compose_msi_msg(irq_data, &msg));
- irq_chip_write_msi_msg(irq_data, &msg);
+ BUG_ON(irq_chip_compose_msi_msg(irq_data, msg));
+ msi_check_level(irq_data->domain, msg);
+ irq_chip_write_msi_msg(irq_data, msg);
return 0;
}

static void msi_domain_deactivate(struct irq_domain *domain,
struct irq_data *irq_data)
{
- struct msi_msg msg;
+ struct msi_msg msg[2];

- memset(&msg, 0, sizeof(msg));
- irq_chip_write_msi_msg(irq_data, &msg);
+ memset(msg, 0, sizeof(msg));
+ irq_chip_write_msi_msg(irq_data, msg);
}

static int msi_domain_alloc(struct irq_domain *domain, unsigned int virq,
--
2.14.2
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