Hi Maxime,
El 11/09/13 04:54, Maxime Ripard escribió:
Hi Emilio,
On Tue, Sep 10, 2013 at 10:43:01PM -0300, Emilio López wrote:
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@xxxxxxxxxxxxx>
---
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).
That looks like a bug in the clock framework. I'd expect it to at least
behave in the same way when disabling the unused clocks at late startup
and when going up disabling some clocks' parent later on.
Yes, I kind of expected the same, and the flag description seems to
imply so too:
#define CLK_IGNORE_UNUSED BIT(3) /* do not gate even if unused */
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.
What was not pretty about it?
It required adding an extra parameter to __clk_disable/__clk_unprepare
to keep track of the call's explicitness, and ignore the
disable/unprepare callback on the implicit case (when
__clk_disable/__clk_unprepare is called recursively) if the flag is set.
This also means adding a wrapping function to at least __clk_unprepare,
so as to to not break callers outside of the clk framework. Overall it
felt too hacky for something that could be properly handled by the
generic code if it had at least 1 user.
I would like to hear Mike's thoughts on this; maybe CLK_IGNORE_UNUSED is
not what we think it should be.
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);
I like this idea as well. But imho, both 1 and 2 should be done. 2) is
only about memory devices, while 1) is much more generic.
And fwiw, the Marvell Armada 370 is also in this case of having a
gatable clock for the DDR that could potentially be disabled (but is
not, since it has no other users than the DDR itself, and as such, no
one ever calls clk_disable on it).
Nice to know, thanks for the information :)
Cheers,
Emilio
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