[PATCH] riscv: dts: sophgo: sg2000-milkv-duo-s: reserve memory for RTOS

[PATCH] riscv: dts: sophgo: sg2000-milkv-duo-s: reserve memory for RTOS

[Andrei Lalaev]

The FSBL loads the coprocessor firmware into the last 2 MB of RAM.
Reserve this region to prevent Linux from using it.

Signed-off-by: Andrei Lalaev <andrey.lalaev@gmail.com>
---
 arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts b/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts
index 78a257839f6f..693c9fd7b771 100644
--- a/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts
+++ b/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts
@@ -22,6 +22,17 @@ chosen {
 		stdout-path = "serial0:115200n8";
 	};
 
+	reserved-memory {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges;
+
+		coprocessor_rtos: region@9fe00000 {
+			reg = <0x9fe00000 0x200000>;
+			no-map;
+		};
+	};
+
 	wifi_pwrseq: wifi-pwrseq {
 		compatible = "mmc-pwrseq-simple";
 		reset-gpios = <&porta 15 GPIO_ACTIVE_LOW>;

---
base-commit: 9b87fdc9af2fbfcdb5c24a64139685ef80f6573f
change-id: 20260916-milkv-duo-s-rtos-memory-7a94933e35bd

Best regards,
--  
Andrei Lalaev <andrey.lalaev@gmail.com>

Re: [PATCH] riscv: dts: sophgo: sg2000-milkv-duo-s: reserve memory for RTOS

[Samuel Holland]

Hi Andrei,

On 2026-09-16 11:06 AM, Andrei Lalaev wrote:
> The FSBL loads the coprocessor firmware into the last 2 MB of RAM.
> Reserve this region to prevent Linux from using it.

If the FSBL wants to reserve some RAM, it should modify the devicetree at
runtime to add that reservation. Adding the reservation here creates an
unnecessary ABI surface between the FSBL and all consumers of the devicetree.

Regards,
Samuel

> Signed-off-by: Andrei Lalaev <andrey.lalaev@gmail.com>
> ---
>  arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts b/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts
> index 78a257839f6f..693c9fd7b771 100644
> --- a/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts
> +++ b/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts
> @@ -22,6 +22,17 @@ chosen {
>  		stdout-path = "serial0:115200n8";
>  	};
>  
> +	reserved-memory {
> +		#address-cells = <1>;
> +		#size-cells = <1>;
> +		ranges;
> +
> +		coprocessor_rtos: region@9fe00000 {
> +			reg = <0x9fe00000 0x200000>;
> +			no-map;
> +		};
> +	};
> +
>  	wifi_pwrseq: wifi-pwrseq {
>  		compatible = "mmc-pwrseq-simple";
>  		reset-gpios = <&porta 15 GPIO_ACTIVE_LOW>;
> 
> ---
> base-commit: 9b87fdc9af2fbfcdb5c24a64139685ef80f6573f
> change-id: 20260916-milkv-duo-s-rtos-memory-7a94933e35bd
> 
> Best regards,
> --  
> Andrei Lalaev <andrey.lalaev@gmail.com>
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH] riscv: dts: sophgo: sg2000-milkv-duo-s: reserve memory for RTOS

[Yao Zi]

On Wed, Sep 16, 2026 at 06:06:30PM +0200, Andrei Lalaev wrote:
> The FSBL loads the coprocessor firmware into the last 2 MB of RAM.
> Reserve this region to prevent Linux from using it.

What if the coprocessor changes the load address, e.g., in a new
release, and how could we support other bootloader implementations
with this modification? Wouldn't the part of memory be wasted if no
coprocessor firmware is loaded at all?

It seems to me the best solution is to modify the FSBL to fix up the
devicetree to reserve memory where the coprocessor firmware is loaded
instead.

Anyway, this reserved region isn't defined by the hardware, thus we
shouldn't include it in the upstream Linux devicetree, since it should
describe the hardware.

> Signed-off-by: Andrei Lalaev <andrey.lalaev@gmail.com>

Best regards.
Yao Zi

Re: [PATCH] riscv: dts: sophgo: sg2000-milkv-duo-s: reserve memory for RTOS

[Inochi Amaoto]

On Wed, Sep 16, 2026 at 12:10:23PM -0500, Samuel Holland wrote:
> Hi Andrei,
> 
> On 2026-09-16 11:06 AM, Andrei Lalaev wrote:
> > The FSBL loads the coprocessor firmware into the last 2 MB of RAM.
> > Reserve this region to prevent Linux from using it.
> 
> If the FSBL wants to reserve some RAM, it should modify the devicetree at
> runtime to add that reservation. Adding the reservation here creates an
> unnecessary ABI surface between the FSBL and all consumers of the devicetree.
> 
> Regards,
> Samuel
> 

This is fair, and the fact is that the current fsbl can disable
coprocessor in its configuration. So I will not take this patch
and maybe do a cleanup for existed devicetree if I have enough
time for it.

Regards,
Inohci

> > Signed-off-by: Andrei Lalaev <andrey.lalaev@gmail.com>
> > ---
> >  arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts b/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts
> > index 78a257839f6f..693c9fd7b771 100644
> > --- a/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts
> > +++ b/arch/riscv/boot/dts/sophgo/sg2000-milkv-duo-s.dts
> > @@ -22,6 +22,17 @@ chosen {
> >  		stdout-path = "serial0:115200n8";
> >  	};
> >  
> > +	reserved-memory {
> > +		#address-cells = <1>;
> > +		#size-cells = <1>;
> > +		ranges;
> > +
> > +		coprocessor_rtos: region@9fe00000 {
> > +			reg = <0x9fe00000 0x200000>;
> > +			no-map;
> > +		};
> > +	};
> > +
> >  	wifi_pwrseq: wifi-pwrseq {
> >  		compatible = "mmc-pwrseq-simple";
> >  		reset-gpios = <&porta 15 GPIO_ACTIVE_LOW>;
> > 
> > ---
> > base-commit: 9b87fdc9af2fbfcdb5c24a64139685ef80f6573f
> > change-id: 20260916-milkv-duo-s-rtos-memory-7a94933e35bd
> > 
> > Best regards,
> > --  
> > Andrei Lalaev <andrey.lalaev@gmail.com>
> > 
> > 
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
> 

Re: [PATCH] riscv: dts: sophgo: sg2000-milkv-duo-s: reserve memory for RTOS

[Andrei Lalaev]

Hi Inochi, Samuel, Yao,

On 17.09.26 04:02, Inochi Amaoto wrote:
> On Wed, Sep 16, 2026 at 12:10:23PM -0500, Samuel Holland wrote:
>> Hi Andrei,
>>
>> On 2026-09-16 11:06 AM, Andrei Lalaev wrote:
>>> The FSBL loads the coprocessor firmware into the last 2 MB of RAM.
>>> Reserve this region to prevent Linux from using it.
>>
>> If the FSBL wants to reserve some RAM, it should modify the devicetree at
>> runtime to add that reservation. Adding the reservation here creates an
>> unnecessary ABI surface between the FSBL and all consumers of the devicetree.
>>
>> Regards,
>> Samuel
>>
> 
> This is fair, and the fact is that the current fsbl can disable
> coprocessor in its configuration. So I will not take this patch
> and maybe do a cleanup for existed devicetree if I have enough
> time for it.

I guess you are right. Just thought that it might have been mistakenly
overlooked for Duo-S because both Duo 64M and Duo 256M have the same
node in their DTSes.
If it is okay with you, I will try remove this node from the DTSes for the
64M/256M variants.

Thank you for the review and sorry for the noise.

 
> Regards,
> Inohci
> 
-- 
Best regards,
Andrei Lalaev