On 09/10/2013 08:43 PM, 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
This would be more accurate:
PLL
|
----------------
| |
DDR Ctrlr Others
|
DDR
So having a DDR controller node with a clock is the right way to do
this. There are other possible needs for describing the DDR controller
such as low power modes and ECC.
Rob
>
> 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);
>
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
