i2c: designware: fix poll-after-enable regression

Not all revisions of DW I2C controller implement the enable status register.
On platforms where that's the case (e.g. BG2CD and SPEAr ARM SoCs), waiting
for enable will time out as reading the unimplemented register yields zero.

It was observed that reading the IC_ENABLE_STATUS register once suffices to
avoid getting it stuck on Bay Trail hardware, so replace polling with one
dummy read of the register.

Fixes: fba4adbbf6 ("i2c: designware: must wait for enable")
Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
Tested-by: Ben Gardner <gardner.ben@gmail.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org

drivers/i2c/busses/i2c-designware-master.c

@@ -209,7 +209,10 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev *dev)
 	i2c_dw_disable_int(dev);
 
 	/* Enable the adapter */
-	__i2c_dw_enable_and_wait(dev, true);
+	__i2c_dw_enable(dev, true);
+
+	/* Dummy read to avoid the register getting stuck on Bay Trail */
+	dw_readl(dev, DW_IC_ENABLE_STATUS);
 
 	/* Clear and enable interrupts */
 	dw_readl(dev, DW_IC_CLR_INTR);