[PATCH 0/3] Fix XIP boot and make XIP testable in QEMU

[PATCH 0/3] Fix XIP boot and make XIP testable in QEMU

[Frederik Haxel]

XIP boot seems to be broken for some time now. A likely reason why no one
seems to have noticed this is that XIP is more difficult to test, as it is
currently not easily testable with QEMU.

These patches fix the XIP boot and allow an XIP build without BUILTIN_DTB,
which in turn makes it easier to test an image with the QEMU virt machine.

Frederik Haxel (3):
  riscv: Make XIP bootable again
  riscv: Fixed wrong register in XIP_FIXUP_FLASH_OFFSET macro
  riscv: Allow disabling of BUILTIN_DTB for XIP

 arch/riscv/Kconfig                 | 6 +++---
 arch/riscv/include/asm/xip_fixup.h | 2 +-
 arch/riscv/kernel/head.S           | 5 ++++-
 arch/riscv/mm/init.c               | 8 ++++++--
 4 files changed, 14 insertions(+), 7 deletions(-)

-- 
2.34.1


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[PATCH 1/3] riscv: Make XIP bootable again

[Frederik Haxel]

Currently, the XIP kernel seems to fail to boot due to missing
XIP_FIXUP and a wrong page_offset value. A superfluous XIP_FIXUP
has also been removed.

Signed-off-by: Frederik Haxel <haxel@fzi.de>
---
 arch/riscv/kernel/head.S | 1 +
 arch/riscv/mm/init.c     | 8 ++++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index b77397432403..a2e2f0dd3899 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -89,6 +89,7 @@ relocate_enable_mmu:
 	/* Compute satp for kernel page tables, but don't load it yet */
 	srl a2, a0, PAGE_SHIFT
 	la a1, satp_mode
+	XIP_FIXUP_OFFSET a1
 	REG_L a1, 0(a1)
 	or a2, a2, a1
 
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 2e011cbddf3a..a65937336cdc 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -174,6 +174,9 @@ void __init mem_init(void)
 
 /* Limit the memory size via mem. */
 static phys_addr_t memory_limit;
+#ifdef CONFIG_XIP_KERNEL
+#define memory_limit	(*(phys_addr_t *)XIP_FIXUP(&memory_limit))
+#endif /* CONFIG_XIP_KERNEL */
 
 static int __init early_mem(char *p)
 {
@@ -952,7 +955,7 @@ static void __init create_fdt_early_page_table(uintptr_t fix_fdt_va,
 	 * setup_vm_final installs the linear mapping. For 32-bit kernel, as the
 	 * kernel is mapped in the linear mapping, that makes no difference.
 	 */
-	dtb_early_va = kernel_mapping_pa_to_va(XIP_FIXUP(dtb_pa));
+	dtb_early_va = kernel_mapping_pa_to_va(dtb_pa);
 #endif
 
 	dtb_early_pa = dtb_pa;
@@ -1055,9 +1058,9 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 #endif
 
 	kernel_map.virt_addr = KERNEL_LINK_ADDR + kernel_map.virt_offset;
-	kernel_map.page_offset = _AC(CONFIG_PAGE_OFFSET, UL);
 
 #ifdef CONFIG_XIP_KERNEL
+	kernel_map.page_offset = PAGE_OFFSET_L3;
 	kernel_map.xiprom = (uintptr_t)CONFIG_XIP_PHYS_ADDR;
 	kernel_map.xiprom_sz = (uintptr_t)(&_exiprom) - (uintptr_t)(&_xiprom);
 
@@ -1067,6 +1070,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 
 	kernel_map.va_kernel_xip_pa_offset = kernel_map.virt_addr - kernel_map.xiprom;
 #else
+	kernel_map.page_offset = _AC(CONFIG_PAGE_OFFSET, UL);
 	kernel_map.phys_addr = (uintptr_t)(&_start);
 	kernel_map.size = (uintptr_t)(&_end) - kernel_map.phys_addr;
 #endif
-- 
2.34.1


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[PATCH 2/3] riscv: Fixed wrong register in XIP_FIXUP_FLASH_OFFSET macro

[Frederik Haxel]

During the refactoring, a bug was introduced in the rarly used
XIP_FIXUP_FLASH_OFFSET macro.

Fixes: bee7fbc38579 ("RISC-V CPU Idle Support")
Fixes: e7681beba992 ("RISC-V: Split out the XIP fixups into their own file")

Signed-off-by: Frederik Haxel <haxel@fzi.de>
---
 arch/riscv/include/asm/xip_fixup.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/xip_fixup.h b/arch/riscv/include/asm/xip_fixup.h
index d4ffc3c37649..b65bf6306f69 100644
--- a/arch/riscv/include/asm/xip_fixup.h
+++ b/arch/riscv/include/asm/xip_fixup.h
@@ -13,7 +13,7 @@
         add \reg, \reg, t0
 .endm
 .macro XIP_FIXUP_FLASH_OFFSET reg
-	la t1, __data_loc
+	la t0, __data_loc
 	REG_L t1, _xip_phys_offset
 	sub \reg, \reg, t1
 	add \reg, \reg, t0
-- 
2.34.1


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[PATCH 3/3] riscv: Allow disabling of BUILTIN_DTB for XIP

[Frederik Haxel]

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>
---
 arch/riscv/Kconfig       | 6 +++---
 arch/riscv/kernel/head.S | 4 +++-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 95a2a06acc6a..72bc31b6eeb9 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -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
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index a2e2f0dd3899..a8939558702c 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -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
-- 
2.34.1


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Re: [PATCH 0/3] Fix XIP boot and make XIP testable in QEMU

[Conor Dooley]

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On Tue, Dec 12, 2023 at 02:01:11PM +0100, Frederik Haxel wrote:
> XIP boot seems to be broken for some time now. A likely reason why no one
> seems to have noticed this is that XIP is more difficult to test, as it is
> currently not easily testable with QEMU.
> 
> These patches fix the XIP boot and allow an XIP build without BUILTIN_DTB,
> which in turn makes it easier to test an image with the QEMU virt machine.


Are you actually using XIP in something other than QEMU? The fact that
some of the blamed fixes are over 18 months old suggests that you are
not actively using XIP builds of the mainline kernel.
There is a desire to remove XIP support (among other things), so if you
do actually have a use case for it, speak up.

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Re: [PATCH 0/3] Fix XIP boot and make XIP testable in QEMU

[Conor Dooley]

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Firstly, no html mails, they're rejected by the lists and break people's
mail flows.

On Tue, Dec 12, 2023 at 03:16:13PM +0100, Vitaly Wool wrote:
> tis 12 dec. 2023 kl. 14:23 skrev Conor Dooley <conor.dooley@microchip.com<mailto:conor.dooley@microchip.com>>:
> > On Tue, Dec 12, 2023 at 02:01:11PM +0100, Frederik Haxel wrote:
> > > XIP boot seems to be broken for some time now. A likely reason why no one
> > > seems to have noticed this is that XIP is more difficult to test, as it is
> > > currently not easily testable with QEMU.
> > >
> > > These patches fix the XIP boot and allow an XIP build without BUILTIN_DTB,
> > > which in turn makes it easier to test an image with the QEMU virt machine.
> > 
> > 
> > Are you actually using XIP in something other than QEMU? The fact that
> > some of the blamed fixes are over 18 months old suggests that you are
> > not actively using XIP builds of the mainline kernel.
> > There is a desire to remove XIP support (among other things), so if you
> > do actually have a use case for it, speak up.
> 
> Yes, we surely do, on K210 for instance. It’s using an older kernel and

The k210 and nommu are on the block for removal too :)
Is your use case for either the k210 or XIP something other than
"ooh this works"? 

> I haven’t checked the mainline status for a while

I figured that when the request I sent asking if you could test XIP was
ignored. We've been 50-50 on whether it has been broken since Alex put
the dtb in the fixmap ~9 months ago.

> but it is likely that I will come up with some XIP updates
> before Christmas.

May I ask what you intend updating?

Cheers,
Conor.

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Re: [PATCH 0/3] Fix XIP boot and make XIP testable in QEMU

[Palmer Dabbelt]

On Tue, 12 Dec 2023 07:14:54 PST (-0800), Conor Dooley wrote:
>
> Firstly, no html mails, they're rejected by the lists and break people's
> mail flows.
>
> On Tue, Dec 12, 2023 at 03:16:13PM +0100, Vitaly Wool wrote:
>> tis 12 dec. 2023 kl. 14:23 skrev Conor Dooley <conor.dooley@microchip.com<mailto:conor.dooley@microchip.com>>:
>> > On Tue, Dec 12, 2023 at 02:01:11PM +0100, Frederik Haxel wrote:
>> > > XIP boot seems to be broken for some time now. A likely reason why no one
>> > > seems to have noticed this is that XIP is more difficult to test, as it is
>> > > currently not easily testable with QEMU.
>> > >
>> > > These patches fix the XIP boot and allow an XIP build without BUILTIN_DTB,
>> > > which in turn makes it easier to test an image with the QEMU virt machine.
>> > 
>> > 
>> > Are you actually using XIP in something other than QEMU? The fact that
>> > some of the blamed fixes are over 18 months old suggests that you are
>> > not actively using XIP builds of the mainline kernel.
>> > There is a desire to remove XIP support (among other things), so if you
>> > do actually have a use case for it, speak up.
>> 
>> Yes, we surely do, on K210 for instance. It’s using an older kernel and
>
> The k210 and nommu are on the block for removal too :)
> Is your use case for either the k210 or XIP something other than
> "ooh this works"? 

Ya, if someone is actually using the XIP (and/or K210 or NOMMU) stuff 
then I'm fine keeping it.  We'd just figured it was probably broken 
because nobody'd been posting patches and we didn't have any automated 
tests.  Looks like it was broken, which is always a pretty strong sign 
it's not being used.

>> I haven’t checked the mainline status for a while
>
> I figured that when the request I sent asking if you could test XIP was
> ignored. We've been 50-50 on whether it has been broken since Alex put
> the dtb in the fixmap ~9 months ago.
>
>> but it is likely that I will come up with some XIP updates
>> before Christmas.
>
> May I ask what you intend updating?
>
> Cheers,
> Conor.

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Re: [PATCH 0/3] Fix XIP boot and make XIP testable in QEMU

[patchwork-bot+linux-riscv]

Hello:

This series was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Tue, 12 Dec 2023 14:01:11 +0100 you wrote:
> XIP boot seems to be broken for some time now. A likely reason why no one
> seems to have noticed this is that XIP is more difficult to test, as it is
> currently not easily testable with QEMU.
> 
> These patches fix the XIP boot and allow an XIP build without BUILTIN_DTB,
> which in turn makes it easier to test an image with the QEMU virt machine.
> 
> [...]

Here is the summary with links:
  - [1/3] riscv: Make XIP bootable again
    https://git.kernel.org/riscv/c/66f1e6809397
  - [2/3] riscv: Fixed wrong register in XIP_FIXUP_FLASH_OFFSET macro
    https://git.kernel.org/riscv/c/5daa37264102
  - [3/3] riscv: Allow disabling of BUILTIN_DTB for XIP
    https://git.kernel.org/riscv/c/6c4a2f6329f0

You are awesome, thank you!
-- 
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