[PATCH 1/4] irqchip/riscv-imsic: Handle non-atomic MSI updates for device

[Anup Patel]

Device having non-atomic MSI update might see an intermediate
state when changing target IMSIC vector from one CPU to another.

To handle such intermediate device state, update MSI address
and MSI data through separate MSI writes to the device.

Fixes: 027e125acdba ("irqchip/riscv-imsic: Add device MSI domain support for platform devices")
Suggested-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Anup Patel <apatel at ventanamicro.com>
---
 drivers/irqchip/irq-riscv-imsic-platform.c | 27 ++++++++++++++++++++++
 drivers/irqchip/irq-riscv-imsic-state.c    | 27 +++++++++++++++++++---
 2 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/irq-riscv-imsic-platform.c b/drivers/irqchip/irq-riscv-imsic-platform.c
index c708780e8760..707c7ccb4d08 100644
--- a/drivers/irqchip/irq-riscv-imsic-platform.c
+++ b/drivers/irqchip/irq-riscv-imsic-platform.c
@@ -97,6 +97,7 @@ static int imsic_irq_set_affinity(struct irq_data *d, const struct cpumask *mask
 {
 	struct imsic_vector *old_vec, *new_vec;
 	struct irq_data *pd = d->parent_data;
+	struct imsic_vector tmp_vec;
 
 	old_vec = irq_data_get_irq_chip_data(pd);
 	if (WARN_ON(!old_vec))
@@ -110,11 +111,37 @@ static int imsic_irq_set_affinity(struct irq_data *d, const struct cpumask *mask
 	if (imsic_vector_get_move(old_vec))
 		return -EBUSY;
 
+	/*
+	 * Device having non-atomic MSI update might see an intermediate
+	 * state when changing target IMSIC vector from one CPU to another.
+	 *
+	 * To avoid losing interrupt to some intermediate state, do the
+	 * following (just like x86 APIC):
+	 *
+	 * 1) First write a temporary IMSIC vector to the device which
+	 * has MSI address same as the old IMSIC vector but MSI data
+	 * matches the new IMSIC vector.
+	 *
+	 * 2) Next write the new IMSIC vector to the device.
+	 *
+	 * Based on the above, the __imsic_local_sync() must check both
+	 * old MSI data and new MSI data on the old CPU for pending
+	 */
+
 	/* Get a new vector on the desired set of CPUs */
 	new_vec = imsic_vector_alloc(old_vec->hwirq, mask_val);
 	if (!new_vec)
 		return -ENOSPC;
 
+	if (new_vec->local_id != old_vec->local_id) {
+		/* Setup temporary vector */
+		tmp_vec.cpu = old_vec->cpu;
+		tmp_vec.local_id = new_vec->local_id;
+
+		/* Point device to the temporary vector */
+		imsic_msi_update_msg(d, &tmp_vec);
+	}
+
 	/* Point device to the new vector */
 	imsic_msi_update_msg(d, new_vec);
 
diff --git a/drivers/irqchip/irq-riscv-imsic-state.c b/drivers/irqchip/irq-riscv-imsic-state.c
index b97e6cd89ed7..230b917136e6 100644
--- a/drivers/irqchip/irq-riscv-imsic-state.c
+++ b/drivers/irqchip/irq-riscv-imsic-state.c
@@ -126,8 +126,8 @@ void __imsic_eix_update(unsigned long base_id, unsigned long num_id, bool pend,
 
 static void __imsic_local_sync(struct imsic_local_priv *lpriv)
 {
-	struct imsic_local_config *mlocal;
-	struct imsic_vector *vec, *mvec;
+	struct imsic_local_config *tlocal, *mlocal;
+	struct imsic_vector *vec, *tvec, *mvec;
 	int i;
 
 	lockdep_assert_held(&lpriv->lock);
@@ -151,7 +151,28 @@ static void __imsic_local_sync(struct imsic_local_priv *lpriv)
 		mvec = READ_ONCE(vec->move);
 		WRITE_ONCE(vec->move, NULL);
 		if (mvec && mvec != vec) {
-			if (__imsic_id_read_clear_pending(i)) {
+			/*
+			 * Device having non-atomic MSI update might see an
+			 * intermediate state so check both old ID and new ID
+			 * for pending interrupts.
+			 *
+			 * For details, refer imsic_irq_set_affinity().
+			 */
+
+			tvec = vec->local_id == mvec->local_id ?
+			       NULL : &lpriv->vectors[mvec->local_id];
+			if (tvec && __imsic_id_read_clear_pending(tvec->local_id)) {
+				/* Retrigger temporary vector if it was already in-use */
+				if (READ_ONCE(tvec->enable)) {
+					tlocal = per_cpu_ptr(imsic->global.local, tvec->cpu);
+					writel_relaxed(tvec->local_id, tlocal->msi_va);
+				}
+
+				mlocal = per_cpu_ptr(imsic->global.local, mvec->cpu);
+				writel_relaxed(mvec->local_id, mlocal->msi_va);
+			}
+
+			if (__imsic_id_read_clear_pending(vec->local_id)) {
 				mlocal = per_cpu_ptr(imsic->global.local, mvec->cpu);
 				writel_relaxed(mvec->local_id, mlocal->msi_va);
 			}
-- 
2.43.0