can: m_can: fix iomap_read_fifo() and iomap_write_fifo()

The read and writes from the fifo are from a buffer, with various
fields and data at predefined offsets. So, they should not be done to
the same address(or port) in case of val_count greater than 1.
Therefore, fix this by using iowrite32()/ioread32() instead of
ioread32_rep()/iowrite32_rep().

Also, the write into FIFO must be performed with an offset from the
message ram base address. Therefore, fix the base address to
mram_base.

Fixes: e39381770e ("can: m_can: Disable IRQs on FIFO bus errors")
Link: https://lore.kernel.org/all/20210920123344.2320-1-a-govindraju@ti.com
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can_platform.c

@@ -32,8 +32,13 @@ static u32 iomap_read_reg(struct m_can_classdev *cdev, int reg)
 static int iomap_read_fifo(struct m_can_classdev *cdev, int offset, void *val, size_t val_count)
 {
 	struct m_can_plat_priv *priv = cdev_to_priv(cdev);
+	void __iomem *src = priv->mram_base + offset;
 
-	ioread32_rep(priv->mram_base + offset, val, val_count);
+	while (val_count--) {
+		*(unsigned int *)val = ioread32(src);
+		val += 4;
+		src += 4;
+	}
 
 	return 0;
 }
@@ -51,8 +56,13 @@ static int iomap_write_fifo(struct m_can_classdev *cdev, int offset,
 			    const void *val, size_t val_count)
 {
 	struct m_can_plat_priv *priv = cdev_to_priv(cdev);
+	void __iomem *dst = priv->mram_base + offset;
 
-	iowrite32_rep(priv->base + offset, val, val_count);
+	while (val_count--) {
+		iowrite32(*(unsigned int *)val, dst);
+		val += 4;
+		dst += 4;
+	}
 
 	return 0;
 }