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riscv: Allow disabling of BUILTIN_DTB for XIP

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This enables, among other things, testing with the QEMU virt machine.

To build an XIP kernel for the QEMU virt machine, configure the
the kernel as desired and apply the following configuration
```
CONFIG_NONPORTABLE=y
CONFIG_XIP_KERNEL=y
CONFIG_XIP_PHYS_ADDR=0x20000000
CONFIG_PHYS_RAM_BASE=0x80200000
CONFIG_BUILTIN_DTB=n
```

Since the QEMU virt flash memory expects a 32 MB file, the built image
must be padded. For example, with
`truncate -s 32M arch/riscv/boot/xipImage`

The kernel can be started using the following command in QEMU (v8+)
```
qemu-system-riscv64 -M virt,pflash0=pflash0 \
 -blockdev node-name=pflash0,driver=file,read-only=on,\
filename=arch/riscv/boot/xipImage <optional parameters>
```

Signed-off-by: Frederik Haxel <haxel@fzi.de>
Link: https://lore.kernel.org/r/20231212130116.848530-4-haxel@fzi.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Frederik Haxel 2023-12-12 14:01:14 +01:00 committed by Palmer Dabbelt
parent 5daa372641
commit 6c4a2f6329
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GPG Key ID: 2E1319F35FBB1889
2 changed files with 6 additions and 4 deletions
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6
arch/riscv/Kconfig
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@ -904,13 +904,13 @@ config RISCV_ISA_FALLBACK
on the replacement properties, "riscv,isa-base" and
"riscv,isa-extensions".
endmenu # "Boot options"
config BUILTIN_DTB
bool
bool "Built-in device tree"
depends on OF && NONPORTABLE
default y if XIP_KERNEL
endmenu # "Boot options"
config PORTABLE
bool
default !NONPORTABLE

4
arch/riscv/kernel/head.S
View File

@ -266,10 +266,12 @@ SYM_CODE_START(_start_kernel)
la sp, _end + THREAD_SIZE
XIP_FIXUP_OFFSET sp
mv s0, a0
mv s1, a1
call __copy_data
/* Restore a0 copy */
/* Restore a0 & a1 copy */
mv a0, s0
mv a1, s1
#endif
#ifndef CONFIG_XIP_KERNEL