i2c: ocores: add polling mode workaround for Sifive FU540-C000 SoC

The i2c-ocore driver already has a polling mode interface.But it needs
a workaround for FU540 Chipset on HiFive unleashed board (RevA00).
There is an erratum in FU540 chip that prevents interrupt driven i2c
transfers from working, and also the I2C controller's interrupt bit
cannot be cleared if set, due to this the existing i2c polling mode
interface added in mainline earlier doesn't work, and CPU stall's
infinitely, when-ever i2c transfer is initiated.

Ref:
	commit dd7dbf0e ("i2c: ocores: refactor setup for polling")

The workaround / fix under OCORES_FLAG_BROKEN_IRQ is particularly for
FU540-COOO SoC.

The polling function identifies a SiFive device based on the device node
and enables the workaround.
Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@sifive.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-ocores.c

@@ -35,6 +35,7 @@ struct ocores_i2c {
 	int iobase;
 	u32 reg_shift;
 	u32 reg_io_width;
+	unsigned long flags;
 	wait_queue_head_t wait;
 	struct i2c_adapter adap;
 	struct i2c_msg *msg;
@@ -84,6 +85,8 @@ struct ocores_i2c {
 #define TYPE_GRLIB		1
 #define TYPE_SIFIVE_REV0	2
 
+#define OCORES_FLAG_BROKEN_IRQ BIT(1) /* Broken IRQ for FU540-C000 SoC */
+
 static void oc_setreg_8(struct ocores_i2c *i2c, int reg, u8 value)
 {
 	iowrite8(value, i2c->base + (reg << i2c->reg_shift));
@@ -236,9 +239,12 @@ static irqreturn_t ocores_isr(int irq, void *dev_id)
 	struct ocores_i2c *i2c = dev_id;
 	u8 stat = oc_getreg(i2c, OCI2C_STATUS);
 
-	if (!(stat & OCI2C_STAT_IF))
+	if (i2c->flags & OCORES_FLAG_BROKEN_IRQ) {
+		if ((stat & OCI2C_STAT_IF) && !(stat & OCI2C_STAT_BUSY))
 			return IRQ_NONE;
-
+	} else if (!(stat & OCI2C_STAT_IF)) {
+		return IRQ_NONE;
+	}
 	ocores_process(i2c, stat);
 
 	return IRQ_HANDLED;
@@ -353,6 +359,11 @@ static void ocores_process_polling(struct ocores_i2c *i2c)
 		ret = ocores_isr(-1, i2c);
 		if (ret == IRQ_NONE)
 			break; /* all messages have been transferred */
+		else {
+			if (i2c->flags & OCORES_FLAG_BROKEN_IRQ)
+				if (i2c->state == STATE_DONE)
+					break;
+		}
 	}
 }
 
@@ -595,6 +606,7 @@ static int ocores_i2c_probe(struct platform_device *pdev)
 {
 	struct ocores_i2c *i2c;
 	struct ocores_i2c_platform_data *pdata;
+	const struct of_device_id *match;
 	struct resource *res;
 	int irq;
 	int ret;
@@ -677,6 +689,14 @@ static int ocores_i2c_probe(struct platform_device *pdev)
 	irq = platform_get_irq(pdev, 0);
 	if (irq == -ENXIO) {
 		ocores_algorithm.master_xfer = ocores_xfer_polling;
+
+		/*
+		 * Set in OCORES_FLAG_BROKEN_IRQ to enable workaround for
+		 * FU540-C000 SoC in polling mode.
+		 */
+		match = of_match_node(ocores_i2c_match, pdev->dev.of_node);
+		if (match && (long)match->data == TYPE_SIFIVE_REV0)
+			i2c->flags |= OCORES_FLAG_BROKEN_IRQ;
 	} else {
 		if (irq < 0)
 			return irq;