linux-kernel - [PATCH v7 4/5] clk: Provide critical clock support

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Date:	Wed, 22 Jul 2015 14:04:14 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:	kernel@...inux.com, mturquette@...aro.org, sboyd@...eaurora.org,
	devicetree@...r.kernel.org, geert@...ux-m68k.org,
	maxime.ripard@...e-electrons.com, s.hauer@...gutronix.de,
	Lee Jones <lee.jones@...aro.org>
Subject: [PATCH v7 4/5] clk: Provide critical clock support

Lots of platforms contain clocks which if turned off would prove fatal.
The only way to recover from these catastrophic failures is to restart
the board(s).  Now, when a clock provider is registered with the
framework it is possible for a list of critical clocks to be supplied
which must be kept ungated.  Each clock mentioned in the newly
introduced 'critical-clock' property will be clk_prepare_enable()d
where the normal references will be taken.  This will prevent the
common clk framework from attempting to gate them during the normal
clk_disable_unused() and disable_clock() procedures.

Note that it will still be possible for knowledgeable drivers to turn
these clocks off using clk_{enable,disable}_critical() calls.

Signed-off-by: Lee Jones <lee.jones@...aro.org>
---
 drivers/clk/clk-conf.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk-conf.c b/drivers/clk/clk-conf.c
index aad4796..f83c1c2 100644
--- a/drivers/clk/clk-conf.c
+++ b/drivers/clk/clk-conf.c
@@ -116,6 +116,45 @@ static int __set_clk_rates(struct device_node *node, bool clk_supplier)
 	return 0;
 }
 
+static int __set_critical_clocks(struct device_node *node, bool clk_supplier)
+{
+	struct of_phandle_args clkspec;
+	struct clk *clk;
+	struct property	*prop;
+	const __be32 *cur;
+	uint32_t index;
+	int ret;
+
+	if (!clk_supplier)
+		return 0;
+
+	of_property_for_each_u32(node, "critical-clock", prop, cur, index) {
+		clkspec.np = node;
+		clkspec.args_count = 1;
+		clkspec.args[0] = index;
+
+		clk = of_clk_get_from_provider(&clkspec);
+		if (IS_ERR(clk)) {
+			pr_err("clk: couldn't get clock %u for %s\n",
+				index, node->full_name);
+			return PTR_ERR(clk);
+		}
+
+		clk_init_critical(clk);
+
+		ret = clk_prepare_enable(clk);
+		if (ret) {
+			pr_err("Failed to enable clock %u for %s: %d\n",
+			       index, node->full_name, ret);
+			return ret;
+		}
+
+		pr_debug("Setting clock as critical %pC\n", clk);
+	}
+
+	return 0;
+}
+
 /**
  * of_clk_set_defaults() - parse and set assigned clocks configuration
  * @node: device node to apply clock settings for
@@ -139,6 +178,10 @@ int of_clk_set_defaults(struct device_node *node, bool clk_supplier)
 	if (rc < 0)
 		return rc;
 
-	return __set_clk_rates(node, clk_supplier);
+	rc = __set_clk_rates(node, clk_supplier);
+	if (rc < 0)
+		return rc;
+
+	return __set_critical_clocks(node, clk_supplier);
 }
 EXPORT_SYMBOL_GPL(of_clk_set_defaults);
-- 
1.9.1

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