[PATCH RFC] of: add a basic memory driver

[Emilio López]

This driver's only job is to claim and ensure that the necessary clock
for memory operation on a DT-enabled machine remains enabled.

Signed-off-by: Emilio López <emilio at elopez.com.ar>
---

Hi,

I am currently facing an issue with the clock setup: a critical but
unclaimed clock gets disabled as a side effect of disabling one of its
children. The clock setup looks something like this:

      PLL
       |
 ------------
 |          |
DDR       Others
            |
          periph

The PLL clock is marked with the CLK_IGNORE_UNUSED flag, so on a normal
boot it remains on, even after the unused clocks cleanup code runs. The
problem occurs when someone enables "periph" and then, later on, disables
it: the framework starts disabling clocks upwards on the tree, 
eventually switching the PLL off (and that kills the machine, as the memory
clock is shut down).

There's two possible solutions I can think of:
 1) add some extra checks on the framework to not turn off clocks marked
    with such a flag on the non-explicit case (ie, when I'm disabling
    some other clock)
 2) create an actual user of the DDR clock, that way it won't get
    disabled simply because it's being used.

I considered 1) and implemented it, but the result was not pretty. This 
patch is my take on 2). Please let me know what you think; all feedback
is welcome :)

Cheers,

Emilio

 drivers/of/Kconfig     |  6 ++++++
 drivers/of/Makefile    |  1 +
 drivers/of/of_memory.c | 30 ++++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+)
 create mode 100644 drivers/of/of_memory.c

diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index 9d2009a..f6c5e20 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -80,4 +80,10 @@ config OF_RESERVED_MEM
 	help
 	  Initialization code for DMA reserved memory
 
+config OF_MEMORY
+	depends on COMMON_CLK
+	def_bool y
+	help
+	  Simple memory initialization
+
 endmenu # OF
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index ed9660a..15f0167 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -10,3 +10,4 @@ obj-$(CONFIG_OF_PCI)	+= of_pci.o
 obj-$(CONFIG_OF_PCI_IRQ)  += of_pci_irq.o
 obj-$(CONFIG_OF_MTD)	+= of_mtd.o
 obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
+obj-$(CONFIG_OF_MEMORY) += of_memory.o
diff --git a/drivers/of/of_memory.c b/drivers/of/of_memory.c
new file mode 100644
index 0000000..a833f7a
--- /dev/null
+++ b/drivers/of/of_memory.c
@@ -0,0 +1,30 @@
+/*
+ * Simple memory driver
+ */
+
+#include <linux/of.h>
+#include <linux/clk.h>
+
+static int __init of_memory_enable(void)
+{
+	struct device_node *np;
+	struct clk *clk;
+
+	np = of_find_node_by_path("/memory");
+	if (!np) {
+		pr_err("no /memory on DT!\n");
+		return 0;
+	}
+
+	clk = of_clk_get(np, 0);
+	if (!IS_ERR(clk)) {
+		clk_prepare_enable(clk);
+		clk_put(clk);
+	}
+
+	of_node_put(np);
+
+	return 0;
+}
+
+device_initcall(of_memory_enable);
-- 
1.8.4