--- zzzz-none-000/linux-3.10.107/arch/mips/dec/ioasic-irq.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/arch/mips/dec/ioasic-irq.c	2021-02-04 17:41:59.000000000 +0000
@@ -1,7 +1,7 @@
 /*
  *	DEC I/O ASIC interrupts.
  *
- *	Copyright (c) 2002, 2003  Maciej W. Rozycki
+ *	Copyright (c) 2002, 2003, 2013  Maciej W. Rozycki
  *
  *	This program is free software; you can redistribute it and/or
  *	modify it under the terms of the GNU General Public License
@@ -51,14 +51,51 @@
 	.irq_unmask = unmask_ioasic_irq,
 };
 
+static void clear_ioasic_dma_irq(struct irq_data *d)
+{
+	u32 sir;
+
+	sir = ~(1 << (d->irq - ioasic_irq_base));
+	ioasic_write(IO_REG_SIR, sir);
+	fast_iob();
+}
+
 static struct irq_chip ioasic_dma_irq_type = {
 	.name = "IO-ASIC-DMA",
-	.irq_ack = ack_ioasic_irq,
+	.irq_ack = clear_ioasic_dma_irq,
 	.irq_mask = mask_ioasic_irq,
-	.irq_mask_ack = ack_ioasic_irq,
 	.irq_unmask = unmask_ioasic_irq,
+	.irq_eoi = clear_ioasic_dma_irq,
 };
 
+/*
+ * I/O ASIC implements two kinds of DMA interrupts, informational and
+ * error interrupts.
+ *
+ * The formers do not stop DMA and should be cleared as soon as possible
+ * so that if they retrigger before the handler has completed, usually as
+ * a side effect of actions taken by the handler, then they are reissued.
+ * These use the `handle_edge_irq' handler that clears the request right
+ * away.
+ *
+ * The latters stop DMA and do not resume it until the interrupt has been
+ * cleared.  This cannot be done until after a corrective action has been
+ * taken and this also means they will not retrigger.  Therefore they use
+ * the `handle_fasteoi_irq' handler that only clears the request on the
+ * way out.  Because MIPS processor interrupt inputs, one of which the I/O
+ * ASIC is cascaded to, are level-triggered it is recommended that error
+ * DMA interrupt action handlers are registered with the IRQF_ONESHOT flag
+ * set so that they are run with the interrupt line masked.
+ *
+ * This mask has `1' bits in the positions of informational interrupts.
+ */
+#define IO_IRQ_DMA_INFO							\
+	(IO_IRQ_MASK(IO_INR_SCC0A_RXDMA) |				\
+	 IO_IRQ_MASK(IO_INR_SCC1A_RXDMA) |				\
+	 IO_IRQ_MASK(IO_INR_ISDN_TXDMA) |				\
+	 IO_IRQ_MASK(IO_INR_ISDN_RXDMA) |				\
+	 IO_IRQ_MASK(IO_INR_ASC_DMA))
+
 void __init init_ioasic_irqs(int base)
 {
 	int i;
@@ -71,7 +108,9 @@
 		irq_set_chip_and_handler(i, &ioasic_irq_type,
 					 handle_level_irq);
 	for (; i < base + IO_IRQ_LINES; i++)
-		irq_set_chip(i, &ioasic_dma_irq_type);
+		irq_set_chip_and_handler(i, &ioasic_dma_irq_type,
+					 1 << (i - base) & IO_IRQ_DMA_INFO ?
+					 handle_edge_irq : handle_fasteoi_irq);
 
 	ioasic_irq_base = base;
 }