mfd: rp1: fix IRQ thread affinity on PREEMPT_RT

rp1_irq_set_affinity() delegates to msi_domain_set_affinity() but
does not call irq_data_update_effective_affinity() and does not
return IRQ_SET_MASK_OK_DONE. Without this, the generic IRQ core
never calls irq_set_thread_affinity(), so on PREEMPT_RT the
force-threaded handler remains pinned to its original CPU even
though the hardware interrupt is steered correctly.

This causes PPS timestamps to be captured on a non-isolated CPU,
adding variable latency to precision timing applications.

Fix by updating the effective affinity and returning
IRQ_SET_MASK_OK_DONE on success.

Fixes: #7301

Signed-off-by: Michael Byczkowski <by@by-online.de>

drivers/mfd/rp1.c

@@ -145,8 +145,14 @@ static int rp1_irq_set_affinity(struct irq_data *irqd, const struct cpumask *des
 {
 	struct rp1_dev *rp1 = irqd->domain->host_data;
 	struct irq_data *pcie_irqd = rp1->pcie_irqds[irqd->hwirq];
+	int ret;
 
-	return msi_domain_set_affinity(pcie_irqd, dest, force);
+	ret = msi_domain_set_affinity(pcie_irqd, dest, force);
+	if (ret >= 0) {
+		irq_data_update_effective_affinity(irqd, dest);
+		return IRQ_SET_MASK_OK_DONE;
+	}
+	return ret;
 }
 
 static struct irq_chip rp1_irq_chip = {