drivers: nvmem: Fix voltage settings for QTI qfprom-efuse

QFPROM controller hardware requires 1.8V min for fuse blowing.
So, this change sets the voltage to 1.8V, required to blow the fuse
for qfprom-efuse controller.

To disable fuse blowing, we set the voltage to 0V since this may
be a shared rail and may be able to run at a lower rate when we're
not blowing fuses.

Fixes: 93b4e49f ("nvmem: qfprom: Add fuse blowing support")
Reported-by: NDouglas Anderson <dianders@chromium.org>
Suggested-by: NDouglas Anderson <dianders@chromium.org>
Reviewed-by: NDouglas Anderson <dianders@chromium.org>
Signed-off-by: NRavi Kumar Bokka <rbokka@codeaurora.org>
Signed-off-by: NSrinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20210330111241.19401-4-srinivas.kandagatla@linaro.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/qfprom.c

@@ -127,6 +127,16 @@ static void qfprom_disable_fuse_blowing(const struct qfprom_priv *priv,
 {
 	int ret;
 
+	/*
+	 * This may be a shared rail and may be able to run at a lower rate
+	 * when we're not blowing fuses.  At the moment, the regulator framework
+	 * applies voltage constraints even on disabled rails, so remove our
+	 * constraints and allow the rail to be adjusted by other users.
+	 */
+	ret = regulator_set_voltage(priv->vcc, 0, INT_MAX);
+	if (ret)
+		dev_warn(priv->dev, "Failed to set 0 voltage (ignoring)\n");
+
 	ret = regulator_disable(priv->vcc);
 	if (ret)
 		dev_warn(priv->dev, "Failed to disable regulator (ignoring)\n");
@@ -172,6 +182,17 @@ static int qfprom_enable_fuse_blowing(const struct qfprom_priv *priv,
 		goto err_clk_prepared;
 	}
 
+	/*
+	 * Hardware requires 1.8V min for fuse blowing; this may be
+	 * a rail shared do don't specify a max--regulator constraints
+	 * will handle.
+	 */
+	ret = regulator_set_voltage(priv->vcc, 1800000, INT_MAX);
+	if (ret) {
+		dev_err(priv->dev, "Failed to set 1.8 voltage\n");
+		goto err_clk_rate_set;
+	}
+
 	ret = regulator_enable(priv->vcc);
 	if (ret) {
 		dev_err(priv->dev, "Failed to enable regulator\n");