On Wed, Dec 08, 2021 at 04:11:23PM +0100, Vincent Whitchurch wrote:
> Add a dtb=<filename> option to boot UML with a devicetree blob. This
> can be used for testing driver code using UML.
Neat!
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
> ---
> arch/um/Kconfig | 1 +
> arch/um/kernel/Makefile | 1 +
> arch/um/kernel/dtb.c | 41 ++++++++++++++++++++++++++++++++++++++++
> arch/um/kernel/um_arch.c | 3 +++
> arch/um/kernel/um_arch.h | 6 ++++++
> 5 files changed, 52 insertions(+)
> create mode 100644 arch/um/kernel/dtb.c
>
> diff --git a/arch/um/Kconfig b/arch/um/Kconfig
> index c18b45f75d41..1cf7ef3a2b81 100644
> --- a/arch/um/Kconfig
> +++ b/arch/um/Kconfig
> @@ -18,6 +18,7 @@ config UML
> select HAVE_DEBUG_KMEMLEAK
> select HAVE_DEBUG_BUGVERBOSE
> select NO_DMA if !UML_DMA_EMULATION
> + select OF_EARLY_FLATTREE
> select GENERIC_IRQ_SHOW
> select GENERIC_CPU_DEVICES
> select HAVE_GCC_PLUGINS
> diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
> index 92692bfef7ae..ebd0cca3ff26 100644
> --- a/arch/um/kernel/Makefile
> +++ b/arch/um/kernel/Makefile
> @@ -22,6 +22,7 @@ obj-y += load_file.o
>
> obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
> obj-$(CONFIG_GPROF) += gprof_syms.o
> +obj-$(CONFIG_OF) += dtb.o
> obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
> obj-$(CONFIG_STACKTRACE) += stacktrace.o
> obj-$(CONFIG_GENERIC_PCI_IOMAP) += ioport.o
> diff --git a/arch/um/kernel/dtb.c b/arch/um/kernel/dtb.c
> new file mode 100644
> index 000000000000..ca69d72025f3
> --- /dev/null
> +++ b/arch/um/kernel/dtb.c
> @@ -0,0 +1,41 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <linux/init.h>
> +#include <linux/of_fdt.h>
> +#include <linux/printk.h>
> +#include <linux/memblock.h>
> +#include <init.h>
> +
> +#include "um_arch.h"
> +
> +static char *dtb __initdata;
> +
> +void uml_dtb_init(void)
> +{
> + long long size;
> + void *area;
> +
> + area = uml_load_file(dtb, &size);
> + if (!area)
> + return;
> +
> + if (!early_init_dt_scan(area)) {
> + pr_err("invalid DTB %s\n", dtb);
> + memblock_free(area, size);
> + return;
> + }
> +
> + unflatten_device_tree();
> + early_init_fdt_scan_reserved_mem();
These should be reversed. early_init_fdt_scan_reserved_mem() works on
the flat tree. Reserved memory needs to be reserved before
unflatten_device_tree() starts allocating memory. Though I imagine that
doesn't really matter for UML.
Also, does the dtb end up in permanently allocated memory (i.e. not
init)? It needs to be if not.
Rob
