[PATCH 02/21] ARM: default machine descriptor for multiplatform

From: Arnd Bergmann
Date: Thu Apr 25 2013 - 13:32:01 EST

Since we now have default implementations for init_time and init_irq,
the init_machine callback is the only one that is not yet optional,
but since simple DT based platforms all have the same
of_platform_populate function call in there, we can consolidate them
as well, and then actually boot with a completely empty machine_desc.
Unofortunately we cannot just default to an empty init_machine: We
cannot call of_platform_populate before init_machine because that
does not work in case of auxdata, and we cannot call it after
init_machine either because the machine might need to run code
after adding the devices.

To take the final step, this adds support for booting without defining
any machine_desc whatsoever.

For the case that CONFIG_MULTIPLATFORM is enabled, it adds a
global machine descriptor that never matches any machine but is
used as a fallback if nothing else matches. We assume that without
CONFIG_MULTIPLATFORM, we only want to boot on the systems that the kernel
is built for, so we still retain the build-time warning for missing
machine descriptors and the run-time warning when the platform does not
match in that case.

In the case that we run on a multiplatform kernel and the machine
provides a fully populated device tree, we attempt to keep booting,
hoping that no machine specific callbacks are necessary.

Finally, this also removes the misguided "select ARCH_VEXPRESS" that
was only added to avoid a build error for allnoconfig kernels.

Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Acked-by: Nicolas Pitre <nico@xxxxxxxxxx>
Acked-by: Olof Johansson <olof@xxxxxxxxx>
Cc: "Russell King - ARM Linux" <linux@xxxxxxxxxxxxxxxx>
Cc: Rob Herring <robherring2@xxxxxxxxx>
arch/arm/Kconfig | 1 -
arch/arm/kernel/devtree.c | 7 +++++++
arch/arm/kernel/setup.c | 11 ++++++++++-
3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index a0d58a6..8c33760 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -890,7 +890,6 @@ config ARCH_MULTI_V7
bool "ARMv7 based platforms (Cortex-A, PJ4, Scorpion, Krait)"
default y
select ARCH_MULTI_V6_V7
select CPU_V7

config ARCH_MULTI_V6_V7
diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
index 70f1bde..5af04f6 100644
--- a/arch/arm/kernel/devtree.c
+++ b/arch/arm/kernel/devtree.c
@@ -180,6 +180,13 @@ struct machine_desc * __init setup_machine_fdt(unsigned int dt_phys)
unsigned long dt_root;
const char *model;

+ DT_MACHINE_START(GENERIC_DT, "Generic DT based system")
+ mdesc_best = (struct machine_desc *)&__mach_desc_GENERIC_DT;
if (!dt_phys)
return NULL;

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 408f446..d039623 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -18,6 +18,7 @@
#include <linux/bootmem.h>
#include <linux/seq_file.h>
#include <linux/screen_info.h>
+#include <linux/of_platform.h>
#include <linux/init.h>
#include <linux/kexec.h>
#include <linux/of_fdt.h>
@@ -672,9 +673,17 @@ struct screen_info screen_info = {

static int __init customize_machine(void)
- /* customizes platform devices, or adds new ones */
+ /*
+ * customizes platform devices, or adds new ones
+ * On DT based machines, we fall back to populating the
+ * machine from the device tree, if no callback is provided,
+ * otherwise we would always need an init_machine callback.
+ */
if (machine_desc->init_machine)
+ else
+ of_platform_populate(NULL, of_default_bus_match_table,
return 0;

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