On Tue, 19 May 2020 23:25:43 +0100
Valentin Schneider [off-list ref] wrote:

On 19/05/20 17:17, Marc Zyngier wrote:

quoted

For irqchips using the fasteoi flow, IPIs are a bit special.

They need to be EOId early (before calling the handler), as
funny things may happen in the handler (they do not necessarily
behave like a normal interrupt), and that the arch code is
already handling the stats.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 include/linux/irq.h |  1 +
 kernel/irq/chip.c   | 26 ++++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 8d5bc2c237d7..726f94d8b8cc 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h

@@ -621,6 +621,7 @@ static inline int irq_set_parent(int irq, int parent_irq)
  */
 extern void handle_level_irq(struct irq_desc *desc);
 extern void handle_fasteoi_irq(struct irq_desc *desc);
+extern void handle_percpu_devid_fasteoi_ipi(struct irq_desc *desc);
 extern void handle_edge_irq(struct irq_desc *desc);
 extern void handle_edge_eoi_irq(struct irq_desc *desc);
 extern void handle_simple_irq(struct irq_desc *desc);

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 41e7e37a0928..7b0b789cfed4 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c

@@ -955,6 +955,32 @@ void handle_percpu_devid_irq(struct irq_desc *desc)
              chip->irq_eoi(&desc->irq_data);
 }

+/**
+ * handle_percpu_devid_fasteoi_ipi - Per CPU local IPI handler with per cpu
+ *				     dev ids
+ * @desc:	the interrupt description structure for this irq
+ *
+ * The biggest differences with the IRQ version are that:
+ * - the interrupt is EOIed early, as the IPI could result in a context
+ *   switch, and we need to make sure the IPI can fire again
+ * - Stats are usually handled at the architecture level, so we ignore them
+ *   here
+ */
+void handle_percpu_devid_fasteoi_ipi(struct irq_desc *desc)
+{
+	struct irq_chip *chip = irq_desc_get_chip(desc);
+	struct irqaction *action = desc->action;
+	unsigned int irq = irq_desc_get_irq(desc);
+	irqreturn_t res;
+  

Tied to the following patch, does that want something like

+	if (!irq_settings_is_no_accounting(desc))
+		__kstat_incr_irqs_this_cpu(desc);
+

While I'm at it, now that we would have IPIs as 'normal' interrupts, what
prevents us from getting rid of the arch-side accounting? Is it just that
we are keeping it as long as handle_IPI() lives, or are there more hurdles
hidden around?

See my reply to Florian. I need to mop the rest of the 32bit irqchips
without having the HW (hip04 is almost a copy of the GIC driver, and
the Marvell horror is very RPi like).

Once this is done, we can kill the home-brewed stuff and rely on core
infrastructure.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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