[PATCH V5] i2c: designware: fix wrong Tx/Rx FIFO for ACPI

[Tin Huynh]

ACPI always sets Tx/Rx FIFO to 32. This configuration will
cause problem if the IP core supports a FIFO size of less than 32.
The driver should read the FIFO size from the IP and select the smaller
one of the two.

Signed-off-by: Tin Huynh <tnhuynh@xxxxxxx>

---
 drivers/i2c/busses/i2c-designware-platdrv.c |   31 ++++++++++++++++++++------
 1 files changed, 24 insertions(+), 7 deletions(-)

Change from V4:
 -Change else condition and add some comments to clarify new approach.

Change from V3:
 -Use uppercase of FIFO instead of lowercase.
 -Correct else condition when IP core return 0 of FIFO.

Change from V2:
 -Add a helper function to set FIFO size.

Change from V1:
 -Revert the default 32 for FIFO, read parameter from IP core
 and pick the smaller one of the two.
 -Correct the title to describe new approach.

diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index 0b42a12..682adc3 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -150,6 +150,29 @@ static int i2c_dw_plat_prepare_clk(struct dw_i2c_dev *i_dev, bool prepare)
 	return 0;
 }
 
+static void dw_i2c_set_fifo_size(struct dw_i2c_dev *dev, int id)
+{
+	u32 param, tx_fifo_depth, rx_fifo_depth;
+
+	/*
+	 * Try to detect the FIFO depth if not set by interface driver,
+	 * the depth could be from 2 to 256 from HW spec.
+	 */
+	param = i2c_dw_read_comp_param(dev);
+	tx_fifo_depth = ((param >> 16) & 0xff) + 1;
+	rx_fifo_depth = ((param >> 8)  & 0xff) + 1;
+	if (!dev->tx_fifo_depth) {
+		dev->tx_fifo_depth = tx_fifo_depth;
+		dev->rx_fifo_depth = rx_fifo_depth;
+		dev->adapter.nr = id;
+	} else if (tx_fifo_depth >= 2) {
+		dev->tx_fifo_depth = min_t(u32, dev->tx_fifo_depth,
+				tx_fifo_depth);
+		dev->rx_fifo_depth = min_t(u32, dev->rx_fifo_depth,
+				rx_fifo_depth);
+	}
+}
+
 static int dw_i2c_plat_probe(struct platform_device *pdev)
 {
 	struct dw_i2c_platform_data *pdata = dev_get_platdata(&pdev->dev);
@@ -246,13 +269,7 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
 				1000000);
 	}
 
-	if (!dev->tx_fifo_depth) {
-		u32 param1 = i2c_dw_read_comp_param(dev);
-
-		dev->tx_fifo_depth = ((param1 >> 16) & 0xff) + 1;
-		dev->rx_fifo_depth = ((param1 >> 8)  & 0xff) + 1;
-		dev->adapter.nr = pdev->id;
-	}
+	dw_i2c_set_fifo_size(dev, pdev->id);
 
 	adap = &dev->adapter;
 	adap->owner = THIS_MODULE;
-- 
1.7.1