1 files changed, 73 insertions, 0 deletions
diff --git a/target/linux/brcm2708/patches-4.4/0431-clk-bcm2835-Mark-the-CM-SDRAM-clock-s-parent-as-crit.patch b/target/linux/brcm2708/patches-4.4/0431-clk-bcm2835-Mark-the-CM-SDRAM-clock-s-parent-as-crit.patch
new file mode 100644
index 0000000000..60ad59dec8
--- /dev/null
+++ b/target/linux/brcm2708/patches-4.4/0431-clk-bcm2835-Mark-the-CM-SDRAM-clock-s-parent-as-crit.patch
@@ -0,0 +1,73 @@
+From 3dbdbeedb865d12700dae53b59e259ea083e6186 Mon Sep 17 00:00:00 2001
+From: Eric Anholt <eric@anholt.net>
+Date: Wed, 1 Jun 2016 12:05:35 -0700
+Subject: [PATCH] clk: bcm2835: Mark the CM SDRAM clock's parent as critical
+
+While the SDRAM is being driven by its dedicated PLL most of the time,
+there is a little loop running in the firmware that periodically turns
+on the CM SDRAM clock (using its pre-initialized parent) and switches
+SDRAM to using the CM clock to do PVT recalibration.
+
+This avoids system hangs if we choose SDRAM's parent for some other
+clock, then disable that clock.
+
+Signed-off-by: Eric Anholt <eric@anholt.net>
+---
+ drivers/clk/bcm/clk-bcm2835.c | 25 +++++++++++++++++++++++++
+ 1 file changed, 25 insertions(+)
+
+--- a/drivers/clk/bcm/clk-bcm2835.c
++++ b/drivers/clk/bcm/clk-bcm2835.c
+@@ -36,6 +36,7 @@
+ 
+ #include <linux/clk-provider.h>
+ #include <linux/clkdev.h>
++#include <linux/clk.h>
+ #include <linux/clk/bcm2835.h>
+ #include <linux/debugfs.h>
+ #include <linux/module.h>
+@@ -1839,6 +1840,25 @@ static const struct bcm2835_clk_desc clk
+ 		.ctl_reg = CM_PERIICTL),
+ };
+ 
++/*
++ * Permanently take a reference on the parent of the SDRAM clock.
++ *
++ * While the SDRAM is being driven by its dedicated PLL most of the
++ * time, there is a little loop running in the firmware that
++ * periodically switches the SDRAM to using our CM clock to do PVT
++ * recalibration, with the assumption that the previously configured
++ * SDRAM parent is still enabled and running.
++ */
++static int bcm2835_mark_sdc_parent_critical(struct clk *sdc)
++{
++	struct clk *parent = clk_get_parent(sdc);
++
++	if (IS_ERR(parent))
++		return PTR_ERR(parent);
++
++	return clk_prepare_enable(parent);
++}
++
+ static int bcm2835_clk_probe(struct platform_device *pdev)
+ {
+ 	struct device *dev = &pdev->dev;
+@@ -1848,6 +1868,7 @@ static int bcm2835_clk_probe(struct plat
+ 	const struct bcm2835_clk_desc *desc;
+ 	const size_t asize = ARRAY_SIZE(clk_desc_array);
+ 	size_t i;
++	int ret;
+ 
+ 	cprman = devm_kzalloc(dev,
+ 			      sizeof(*cprman) + asize * sizeof(*clks),
+@@ -1878,6 +1899,10 @@ static int bcm2835_clk_probe(struct plat
+ 			clks[i] = desc->clk_register(cprman, desc->data);
+ 	}
+ 
++	ret = bcm2835_mark_sdc_parent_critical(clks[BCM2835_CLOCK_SDRAM]);
++	if (ret)
++		return ret;
++
+ 	return of_clk_add_provider(dev->of_node, of_clk_src_onecell_get,
+ 				   &cprman->onecell);
+ }