[PATCH] MIPS: add generic device tree 2nd stage support

[Sascha Hauer]

On Mon, Mar 11, 2024 at 12:54:34AM +0300, Antony Pavlov wrote:
> Building and running barebox for 32-bit malta:
> 
> export ARCH=mips
> export CROSS_COMPILE=mips-linux-gnu-
> make -s qemu-malta_defconfig
> sed -i "s/# \(CONFIG_BOARD_MIPS_GENERIC_DT\) is not set/\1=y/" .config
> make -s oldconfig
> make -s
> qemu-system-mips -M malta -cpu 24Kf -m 256M \
>             -nographic -serial mon:stdio \
>             -bios images/barebox-qemu-malta.img \
>             -net user,tftp=$(pwd) -net nic,model=e1000
> 
> Building and running barebox for 64-bit malta:
> 
> export ARCH=mips
> export CROSS_COMPILE=mips-linux-gnu-
> make -s qemu-malta64el_defconfig
> sed -i "s/# \(CONFIG_BOARD_MIPS_GENERIC_DT\) is not set/\1=y/" .config
> make -s oldconfig
> make -s
> qemu-system-mips64el -M malta -cpu MIPS64R2-generic -m 256M \
>             -nographic -serial mon:stdio \
>             -bios images/barebox-qemu-malta.img.swapped \
>             -net user,tftp=$(pwd) -net nic,model=e1000
> 
> Use bootm to run barebox-dt-2nd.img (external device tree):
> 
> barebox at qemu malta:/ dhcp
> barebox at qemu malta:/ cp /mnt/tftp/images/barebox-dt-2nd.img barebox.img
> barebox at qemu malta:/ cp /mnt/tftp/arch/mips/dts/qemu-malta.dtb .
> barebox at qemu malta:/ imd barebox.img
> barebox at qemu malta:/ bootm -o qemu-malta.dtb barebox.img
> 
> Use bootm to run barebox-qemu-malta.img (encapsulated device tree):
> 
> barebox at qemu malta:/ dhcp
> barebox at qemu malta:/ cp /mnt/tftp/images/barebox-qemu-malta.img barebox.img
> barebox at qemu malta:/ imd barebox.img
> barebox at qemu malta:/ bootm barebox.img
> 
> N.B. Use just the same commands for both 32-bit and 64-bit malta boards.
> 
> Signed-off-by: Antony Pavlov <antonynpavlov at gmail.com>
> ---
>  arch/mips/Kconfig               | 10 ++++++++++
>  arch/mips/boards/Makefile       |  2 ++
>  arch/mips/boards/board-dt-2nd.S | 35 +++++++++++++++++++++++++++++++++
>  arch/mips/boot/main_entry-pbl.c |  4 ++++
>  arch/mips/lib/bootm.c           | 13 ++++++++++--
>  5 files changed, 62 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 63ba6aa9d5a..14062dee347 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -319,6 +319,16 @@ config 64BIT
>  
>  endchoice
>  
> +config BOARD_MIPS_GENERIC_DT
> +	select BOARD_GENERIC_DT
> +	depends on OFDEVICE
> +	bool "Build generic MIPS device tree 2nd stage image"
> +	help
> +	  This enables compilation of a generic image that can be started 2nd
> +	  stage from barebox or from qemu. It picks up a device tree passed
> +	  in a1 like the Kernel does.
> +	  The image will be called images/barebox-dt-2nd.img
> +
>  menu "MIPS specific settings"
>  
>  config CMD_MIPS_CPUINFO
> diff --git a/arch/mips/boards/Makefile b/arch/mips/boards/Makefile
> index 9402035856c..c4ce599c934 100644
> --- a/arch/mips/boards/Makefile
> +++ b/arch/mips/boards/Makefile
> @@ -13,3 +13,5 @@ obj-$(CONFIG_BOARD_QEMU_MALTA) += qemu-malta/
>  obj-$(CONFIG_BOARD_RZX50) += ritmix-rzx50/
>  obj-$(CONFIG_BOARD_TPLINK_MR3020) += tplink-mr3020/
>  obj-$(CONFIG_BOARD_TPLINK_WDR4300) += tplink-wdr4300/
> +
> +pbl-$(CONFIG_BOARD_MIPS_GENERIC_DT) += board-dt-2nd.o
> diff --git a/arch/mips/boards/board-dt-2nd.S b/arch/mips/boards/board-dt-2nd.S
> new file mode 100644
> index 00000000000..a1465f09e36
> --- /dev/null
> +++ b/arch/mips/boards/board-dt-2nd.S
> @@ -0,0 +1,35 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Startup Code for generic MIPS device tree 2nd stage image
> + *
> + * Copyright (C) 2024 Antony Pavlov <antonynpavlov at gmail.com>
> + */
> +
> +#include <asm/asm.h>
> +#include <asm/pbl_macros.h>
> +#include <linux/sizes.h>
> +
> +ENTRY_FUNCTION(start_dt_2nd)
> +
> +	/* save device tree address in v1 */
> +	move	v1, a1
> +
> +	mips_cpu_setup
> +
> +	copy_to_link_location	start_dt_2nd
> +
> +	stack_setup
> +
> +	/* pbl_main_entry() computes fdt_len by itself
> +	 * if fdt == fdt_end */
> +	move	a0, v1 /* fdt */
> +	move	a1, v1 /* fdt_end */
> +	PTR_LI	a2, SZ_256M /* ram_size */

Could this be taken from dt finally? I think it's good enough for now,
but would be a nice improvement.

Sascha

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