[RFC PATCHv2] ARM: mvebu: Let the device-tree determine smp_ops

[Maxime Ripard]

Hi,

On Tue, Nov 18, 2014 at 12:34:41PM +1300, Chris Packham wrote:
> Hi Thomas, Maxime
> 
> On Mon, 17 Nov 2014, Thomas Petazzoni wrote:
> 
> >Dear Chris Packham,
> >
> >On Fri,  7 Nov 2014 15:33:46 +1300, Chris Packham wrote:
> >>The machine specific SMP operations can be configured either via
> >>setup_arch or via arm_dt_init_cpu_maps. For the ARMADA_370_XP_DT devices
> >>both of these are called and setup_arch wins because it is called last.
> >>This means that it is not possible to substitute a different set of SMP
> >>operations via the device-tree.
> >>
> >>For the ARMADA_370_XP_DT compatible devices add a smp_init function that
> >>detects if the device tree has an enable-method defined. If it does
> >>return true to indicate that the smp_ops have already been set which
> >>will prevent setup_arch from overriding them.
> >>
> >>Signed-off-by: Chris Packham <chris.packham at alliedtelesis.co.nz>
> >
> >My colleague Maxime Ripard (in Cc) rightfully suggests exploring a
> >different option: what about getting rid completely of the .smp field
> >of the DT_MACHINE structure, and instead have some code run early
> >enough that looks if an enable-method is defined, and if not, defines
> >it to the default value. This way, we continue to be backward
> >compatible in terms of DT, but we always use the enable-method from the
> >DT, and not sometimes from DT, sometimes from the DT_MACHINE structure.
> >
> >Unfortunately, it will have to be done on the flattened DT, because the
> >DT is unflattened right before the enable-method properties are looked
> >up:
> >
> >       unflatten_device_tree();
> >
> >       arm_dt_init_cpu_maps();
> >
> >And manipulating the DT in its flattened format, while possible in
> >->dt_fixup(), is a pain, and probably doesn't allow adding new
> >properties anyway.
> >
> >So, in the end, maybe this idea doesn't work, I haven't checked
> >completely.
> >
> 
> So yeah it's tricky to work with the flattened dt. Not impossible the
> powerpc arch code does quite a lot with it. Arm does less but still uses it
> in atags_to_fdt.c. Below is a rough attempt at an implementation that seems
> to work. Because of the flattened dt it's harder to iterate through the cpu
> nodes so I haven't implemented anything to look for an enable-method
> attached to them.
> 
> ---- 8< ----
> Subject: [PATCH] ARM: mvebu: use dt_fixup to provide fallback for
>  enable-method
> 
> When the device tree doesn't define an enable-method insert a property
> into the flattened device tree. arm_dt_init_cpu_maps() will then parse
> this an set smp_ops appropriately. Now that we have this fallback it is
> no longer necessary to set .smp in the DT_MACHINE definition.
> 
> Signed-off-by: Chris Packham <chris.packham at alliedtelesis.co.nz>
> ---
>  arch/arm/mach-mvebu/Makefile   |  2 ++
>  arch/arm/mach-mvebu/board-v7.c | 23 ++++++++++++++++++++++-
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-mvebu/Makefile b/arch/arm/mach-mvebu/Makefile
> index 1636cdb..f818eaf 100644
> --- a/arch/arm/mach-mvebu/Makefile
> +++ b/arch/arm/mach-mvebu/Makefile
> @@ -14,3 +14,5 @@ endif
> 
>  obj-$(CONFIG_MACH_DOVE)		 += dove.o
>  obj-$(CONFIG_MACH_KIRKWOOD)	 += kirkwood.o kirkwood-pm.o
> +
> +CFLAGS_board-v7.o = -I$(src)/../../../scripts/dtc/libfdt
> \ No newline at end of file
> diff --git a/arch/arm/mach-mvebu/board-v7.c b/arch/arm/mach-mvebu/board-v7.c
> index b2524d6..45851a2 100644
> --- a/arch/arm/mach-mvebu/board-v7.c
> +++ b/arch/arm/mach-mvebu/board-v7.c
> @@ -17,6 +17,8 @@
>  #include <linux/clk-provider.h>
>  #include <linux/of_address.h>
>  #include <linux/of_platform.h>
> +#include <linux/of_fdt.h>
> +#include <linux/libfdt.h>
>  #include <linux/io.h>
>  #include <linux/clocksource.h>
>  #include <linux/dma-mapping.h>
> @@ -184,6 +186,25 @@ static void __init mvebu_dt_init(void)
>  	of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
>  }
> 
> +static void __init armada_370_xp_dt_fixup(void)
> +{
> +	void *prop;
> +	int offset;
> +	int len;
> +
> +	offset = fdt_path_offset(initial_boot_params, "/cpus");
> +	prop = fdt_getprop(initial_boot_params, offset, "enable-method", &len);
> +
> +	if (!prop) {
> +		pr_info("No enable-method defined. "
> +			"Falling back to \"marvell,armada-xp-smp\"\n");
> +
> +		fdt_appendprop(initial_boot_params, offset, "enable-method",
> +			       "marvell,armada-xp-smp",
> +			       sizeof("marvell,armada-xp-smp"));
> +	}
> +}
> +

It's what I had in mind yes :)

I don't think you need to use fdt_appendprop though, fdt_setprop would
be enough.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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