[PATCH] riscv: qemu: Remove fdt_high default

[PATCH] riscv: qemu: Remove fdt_high default

[Vivian Wang]

Setting fdt_high to all ones is discouraged and does not appear to be
useful for RISC-V QEMU. Moreover, it causes a boot failure when the FDT
generated internally by QEMU is used while booting. Remove it to allow
U-Boot to pick a suitable address and relocate the FDT.

Closes: https://lore.kernel.org/u-boot/8397369a-9b0b-4798-9c30-3a81165657d6@iscas.ac.cn
Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>
---
 include/configs/qemu-riscv.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/configs/qemu-riscv.h b/include/configs/qemu-riscv.h
index cf4fcb90b047bb641d702124f2efa451408c0b16..dad59cc0d5827981396b10d9782766d4d9aa29c6 100644
--- a/include/configs/qemu-riscv.h
+++ b/include/configs/qemu-riscv.h
@@ -32,7 +32,6 @@
 
 #define CFG_EXTRA_ENV_SETTINGS \
 	CFG_STD_DEVICES_SETTINGS \
-	"fdt_high=0xffffffffffffffff\0" \
 	"initrd_high=0xffffffffffffffff\0" \
 	"kernel_addr_r=0x84000000\0" \
 	"kernel_comp_addr_r=0x88000000\0" \

---
base-commit: 18973d4b0801ec6d7fddc0084601036b5c3b08ad
change-id: 20250915-qemu-riscv-remove-fdt-high-1ac688dd13bb

Best regards,
-- 
Vivian "dramforever" Wang

Re: [PATCH] riscv: qemu: Remove fdt_high default

[Tom Rini]

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On Mon, Sep 15, 2025 at 07:45:49AM +0800, Vivian Wang wrote:

> Setting fdt_high to all ones is discouraged and does not appear to be
> useful for RISC-V QEMU. Moreover, it causes a boot failure when the FDT
> generated internally by QEMU is used while booting. Remove it to allow
> U-Boot to pick a suitable address and relocate the FDT.
> 
> Closes: https://lore.kernel.org/u-boot/8397369a-9b0b-4798-9c30-3a81165657d6@iscas.ac.cn
> Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>

I'm very glad to see this finally and would like to see the rest of the
RISC-V platforms follow and do the same now.

Reviewed-by: Tom Rini <trini@konsulko.com>

-- 
Tom

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Re: [PATCH] riscv: qemu: Remove fdt_high default

[E Shattow]

Hi Tom,  Add CC: Heinrich

On 9/15/25 07:32, Tom Rini wrote:
> On Mon, Sep 15, 2025 at 07:45:49AM +0800, Vivian Wang wrote:
> 
>> Setting fdt_high to all ones is discouraged and does not appear to be
>> useful for RISC-V QEMU. Moreover, it causes a boot failure when the FDT
>> generated internally by QEMU is used while booting. Remove it to allow
>> U-Boot to pick a suitable address and relocate the FDT.
>>
>> Closes: https://lore.kernel.org/u-boot/8397369a-9b0b-4798-9c30-3a81165657d6@iscas.ac.cn
>> Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>
> 

> I'm very glad to see this finally and would like to see the rest of the
> RISC-V platforms follow and do the same now.
> 
> Reviewed-by: Tom Rini <trini@konsulko.com>
> 

When you say you would like the rest of the RISC-V platforms (to) follow
and do the same;  What do you mean?  Heinrich and I were trying to
figure this out off of something you said on IRC awhile back. I was
taking a guess it was the qemu config (and this patch makes sense to me
so I think that's part of it), but what else? Is that a reference to
sifive-unleashed config fragment, are there others?

If you give us a detailed hint what we should be looking at it would go
a long way and we can test / figure out the rest. Is initrd_high
all-ones on your radar too?

Thanks,

-E Shattow

Re: [PATCH] riscv: qemu: Remove fdt_high default

[Tom Rini]

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On Mon, Sep 15, 2025 at 05:25:23PM -0700, E Shattow wrote:
> Hi Tom,  Add CC: Heinrich
> 
> On 9/15/25 07:32, Tom Rini wrote:
> > On Mon, Sep 15, 2025 at 07:45:49AM +0800, Vivian Wang wrote:
> > 
> >> Setting fdt_high to all ones is discouraged and does not appear to be
> >> useful for RISC-V QEMU. Moreover, it causes a boot failure when the FDT
> >> generated internally by QEMU is used while booting. Remove it to allow
> >> U-Boot to pick a suitable address and relocate the FDT.
> >>
> >> Closes: https://lore.kernel.org/u-boot/8397369a-9b0b-4798-9c30-3a81165657d6@iscas.ac.cn
> >> Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>
> > 
> 
> > I'm very glad to see this finally and would like to see the rest of the
> > RISC-V platforms follow and do the same now.
> > 
> > Reviewed-by: Tom Rini <trini@konsulko.com>
> > 
> 
> When you say you would like the rest of the RISC-V platforms (to) follow
> and do the same;  What do you mean?  Heinrich and I were trying to
> figure this out off of something you said on IRC awhile back. I was
> taking a guess it was the qemu config (and this patch makes sense to me
> so I think that's part of it), but what else? Is that a reference to
> sifive-unleashed config fragment, are there others?
> 
> If you give us a detailed hint what we should be looking at it would go
> a long way and we can test / figure out the rest. Is initrd_high
> all-ones on your radar too?

The simple answer is that no platforms should ever set fdt_high=0xff...
nor initrd_high=0xff... by default. This tells U-Boot to never try and
relocate in memory these parts of the boot even when U-Boot knows that
they will overlap or are not correctly aligned. This in turn leads to
harder to debug failures at run time. Unfortunately RISC-V platforms
were introduced with these set and whatever checkpatch.pl check I had
missed them at the time (aside, most recently checkpatch.pl was missing
this in .env files, I fixed that today).

-- 
Tom

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Re: [PATCH] riscv: qemu: Remove fdt_high default

[Auer, Lukas]

On Mon, 2025-09-15 at 07:45 +0800, Vivian Wang wrote:
> Setting fdt_high to all ones is discouraged and does not appear to be
> useful for RISC-V QEMU. Moreover, it causes a boot failure when the FDT
> generated internally by QEMU is used while booting. Remove it to allow
> U-Boot to pick a suitable address and relocate the FDT.
> 
> Closes: https://lore.kernel.org/u-boot/8397369a-9b0b-4798-9c30-3a81165657d6@iscas.ac.cn
> Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>
> ---
>  include/configs/qemu-riscv.h | 1 -
>  1 file changed, 1 deletion(-)

Looks good!

Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>

Re: [PATCH] riscv: qemu: Remove fdt_high default

[Leo Liang]

On Mon, Sep 15, 2025 at 07:45:49AM +0800, Vivian Wang wrote:
> Setting fdt_high to all ones is discouraged and does not appear to be
> useful for RISC-V QEMU. Moreover, it causes a boot failure when the FDT
> generated internally by QEMU is used while booting. Remove it to allow
> U-Boot to pick a suitable address and relocate the FDT.
> 
> Closes: https://lore.kernel.org/u-boot/8397369a-9b0b-4798-9c30-3a81165657d6@iscas.ac.cn
> Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>
> Reviewed-by: Tom Rini <trini@konsulko.com>
> Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
> ---
>  include/configs/qemu-riscv.h | 1 -
>  1 file changed, 1 deletion(-)

Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>