[PATCH 3/6] clk: bcm2835: enable clocks that have been enabled by firmware

kernel at martin.sperl.org kernel at martin.sperl.org
Mon Feb 29 03:39:19 PST 2016

From: Martin Sperl <kernel at martin.sperl.org>

If a clock that has been enabled by the firmware gets disabled
by a driver this may right now result in a crash of the system
as then also the corresponding PLL_dividers as well as PLLs
get disabled (if not used) - some of which are used by the
VideoCore GPU (which also runs the firmware)

This patch prepares/enables those clocks that have been
configured by the firmware.

Whenever the clock framework implements either
CLK_IS_CRITICAL or HAND_OFF this can get changed to use this
new mechanism.

For this to be completely successful (i.e not missing a clock
and subsequently a pll) it is recommended to add all the known
clocks of the soc so that this can get applied to all clocks.

Signed-off-by: Martin Sperl <kernel at martin.sperl.org>
 drivers/clk/bcm/clk-bcm2835.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
index 30d6486..1fbb55d 100644
--- a/drivers/clk/bcm/clk-bcm2835.c
+++ b/drivers/clk/bcm/clk-bcm2835.c
@@ -37,6 +37,7 @@
  * generator).

+#include <linux/clk.h>
 #include <linux/clk-provider.h>
 #include <linux/clkdev.h>
 #include <linux/clk/bcm2835.h>
@@ -1478,6 +1479,7 @@ static struct clk *bcm2835_register_clock(struct bcm2835_cprman *cprman,
 	struct clk_init_data init;
 	const char *parents[1 << CM_SRC_BITS];
 	size_t i;
+	struct clk *clk;

 	 * Replace our "xosc" references with the oscillator's
@@ -1511,7 +1513,18 @@ static struct clk *bcm2835_register_clock(struct bcm2835_cprman *cprman,
 	clock->data = data;
 	clock->hw.init = &init;

-	return devm_clk_register(cprman->dev, &clock->hw);
+	clk = devm_clk_register(cprman->dev, &clock->hw);
+	if (IS_ERR_OR_NULL(clk))
+		return clk;
+	/* enable/prepare if the clock is enabled by the firmware */
+	if (cprman_read(cprman, data->ctl_reg) & CM_ENABLE) {
+		dev_info(cprman->dev,
+			 "found firmware enabled clock %pC\n", clk);
+		clk_prepare_enable(clk);
+	}
+	return clk;

 static int bcm2835_clk_probe(struct platform_device *pdev)

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