clk: qcom: Support 'protected-clocks' property

Certain firmware configurations "protect" clks and cause the entire
system to reboot when a non-secure OS such as Linux tries to read or
write protected clk registers. But other firmware configurations allow
reading or writing the same registers, and they may actually require
that the OS use the otherwise locked down clks. Support the
'protected-clocks' property by never registering these protected clks
with the common clk framework. This way, when firmware is protecting
these clks we won't have the chance to ever read or write these
registers and take down the entire system.

Cc: Taniya Das <tdas@codeaurora.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/qcom/common.c

@@ -191,6 +191,22 @@ int qcom_cc_register_sleep_clk(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(qcom_cc_register_sleep_clk);
 
+/* Drop 'protected-clocks' from the list of clocks to register */
+static void qcom_cc_drop_protected(struct device *dev, struct qcom_cc *cc)
+{
+	struct device_node *np = dev->of_node;
+	struct property *prop;
+	const __be32 *p;
+	u32 i;
+
+	of_property_for_each_u32(np, "protected-clocks", prop, p, i) {
+		if (i >= cc->num_rclks)
+			continue;
+
+		cc->rclks[i] = NULL;
+	}
+}
+
 static struct clk_hw *qcom_cc_clk_hw_get(struct of_phandle_args *clkspec,
 					 void *data)
 {
@@ -251,6 +267,8 @@ int qcom_cc_really_probe(struct platform_device *pdev,
 	cc->rclks = rclks;
 	cc->num_rclks = num_clks;
 
+	qcom_cc_drop_protected(dev, cc);
+
 	for (i = 0; i < num_clks; i++) {
 		if (!rclks[i])
 			continue;