mtd: pxa3xx-nand: handle PIO in threaded interrupt

Change the handling of the data stage in the driver : don't pump data in
the top-half interrupt, but rather schedule a thread for non dma cases.

This will enable latencies in the data pumping, especially if delays are
required. Moreover platform shall be more reactive as other interrupts
can be served while pumping data.

No throughput degradation was observed, at least on the zylonite
platform, while a slight degradation was being expected.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Tested-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/pxa3xx_nand.c

@@ -605,11 +605,24 @@ static void start_data_dma(struct pxa3xx_nand_info *info)
 {}
 #endif
 
+static irqreturn_t pxa3xx_nand_irq_thread(int irq, void *data)
+{
+	struct pxa3xx_nand_info *info = data;
+
+	handle_data_pio(info);
+
+	info->state = STATE_CMD_DONE;
+	nand_writel(info, NDSR, NDSR_WRDREQ | NDSR_RDDREQ);
+
+	return IRQ_HANDLED;
+}
+
 static irqreturn_t pxa3xx_nand_irq(int irq, void *devid)
 {
 	struct pxa3xx_nand_info *info = devid;
 	unsigned int status, is_completed = 0, is_ready = 0;
 	unsigned int ready, cmd_done;
+	irqreturn_t ret = IRQ_HANDLED;
 
 	if (info->cs == 0) {
 		ready           = NDSR_FLASH_RDY;
@@ -651,7 +664,8 @@ static irqreturn_t pxa3xx_nand_irq(int irq, void *devid)
 		} else {
 			info->state = (status & NDSR_RDDREQ) ?
 				      STATE_PIO_READING : STATE_PIO_WRITING;
-			handle_data_pio(info);
+			ret = IRQ_WAKE_THREAD;
+			goto NORMAL_IRQ_EXIT;
 		}
 	}
 	if (status & cmd_done) {
@@ -692,7 +706,7 @@ static irqreturn_t pxa3xx_nand_irq(int irq, void *devid)
 	if (is_ready)
 		complete(&info->dev_ready);
 NORMAL_IRQ_EXIT:
-	return IRQ_HANDLED;
+	return ret;
 }
 
 static inline int is_buf_blank(uint8_t *buf, size_t len)
@@ -1708,7 +1722,9 @@ static int alloc_nand_resource(struct platform_device *pdev)
 	/* initialize all interrupts to be disabled */
 	disable_int(info, NDSR_MASK);
 
-	ret = request_irq(irq, pxa3xx_nand_irq, 0, pdev->name, info);
+	ret = request_threaded_irq(irq, pxa3xx_nand_irq,
+				   pxa3xx_nand_irq_thread, IRQF_ONESHOT,
+				   pdev->name, info);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "failed to request IRQ\n");
 		goto fail_free_buf;