[PATCH 4.16 15/43] phy: qcom-qusb2: Fix crash if nvmem cell not specified

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Manu Gautam <mgautam@codeaurora.org>

commit 0b4555e776ba0712c6fafb98b226b21fd05d2427 upstream.

Driver currently crashes due to NULL pointer deference
while updating PHY tune register if nvmem cell is NULL.
Since, fused value for Tune1/2 register is optional,
we'd rather bail out.

Fixes: ca04d9d3e1b1 ("phy: qcom-qusb2: New driver for QUSB2 PHY on Qcom chips")
Reviewed-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Reviewed-by: Evan Green <evgreen@chromium.org>
Cc: stable <stable@vger.kernel.org> # 4.14+
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/phy/qualcomm/phy-qcom-qusb2.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/phy/qualcomm/phy-qcom-qusb2.c
+++ b/drivers/phy/qualcomm/phy-qcom-qusb2.c
@@ -178,6 +178,10 @@ static void qusb2_phy_set_tune2_param(st
 	struct device *dev = &qphy->phy->dev;
 	u8 *val;
 
+	/* efuse register is optional */
+	if (!qphy->cell)
+		return;
+
 	/*
 	 * Read efuse register having TUNE2 parameter's high nibble.
 	 * If efuse register shows value as 0x0, or if we fail to find