[PATCH v2] riscv: Fix detecting FPU support in standard extension

[PATCH v2] riscv: Fix detecting FPU support in standard extension

[Yu Chien Peter Lin]

We should check the string until it hits underscore, in case it
searches for the letters in the custom extension. For example,
"rv64imac_xandes" will be treated as D extension support since
there is a "d" in "andes", resulting illegal instruction caused
by initializing FCSR.

Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
---
 arch/riscv/cpu/cpu.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
index 52ab02519f..d34c8efce0 100644
--- a/arch/riscv/cpu/cpu.c
+++ b/arch/riscv/cpu/cpu.c
@@ -36,6 +36,7 @@ static inline bool supports_extension(char ext)
 #ifdef CONFIG_CPU
 	struct udevice *dev;
 	char desc[32];
+	int i;
 
 	uclass_find_first_device(UCLASS_CPU, &dev);
 	if (!dev) {
@@ -43,9 +44,16 @@ static inline bool supports_extension(char ext)
 		return false;
 	}
 	if (!cpu_get_desc(dev, desc, sizeof(desc))) {
-		/* skip the first 4 characters (rv32|rv64) */
-		if (strchr(desc + 4, ext))
-			return true;
+		/*
+		 * skip the first 4 characters (rv32|rv64) and
+		 * check until underscore
+		 */
+		for (i = 4; i < sizeof(desc); i++) {
+			if (desc[i] == '_' || desc[i] == '\0')
+				break;
+			if (desc[i] == ext)
+				return true;
+		}
 	}
 
 	return false;
-- 
2.34.1

Re: [PATCH v2] riscv: Fix detecting FPU support in standard extension

[Rick Chen]

> From: U-Boot <u-boot-bounces@lists.denx.de> On Behalf Of Yu Chien Peter Lin
> Sent: Saturday, November 05, 2022 2:02 PM
> To: u-boot@lists.denx.de
> Cc: samuel@sholland.org; Peter Yu-Chien Lin(林宇謙) <peterlin@andestech.com>
> Subject: [PATCH v2] riscv: Fix detecting FPU support in standard extension
>
> We should check the string until it hits underscore, in case it searches for the letters in the custom extension. For example, "rv64imac_xandes" will be treated as D extension support since there is a "d" in "andes", resulting illegal instruction caused by initializing FCSR.
>
> Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
> ---
>  arch/riscv/cpu/cpu.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)

Reviewed-by: Rick Chen <rick@andestech.com>

Re: [PATCH v2] riscv: Fix detecting FPU support in standard extension

[Padmarao.Begari]

> On Sat, 2022-11-05 at 14:02 +0800, Yu Chien Peter Lin wrote:
> 
> We should check the string until it hits underscore, in case it
> searches for the letters in the custom extension. For example,
> "rv64imac_xandes" will be treated as D extension support since
> there is a "d" in "andes", resulting illegal instruction caused
> by initializing FCSR.
> 
> Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
> ---
>  arch/riscv/cpu/cpu.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
> index 52ab02519f..d34c8efce0 100644
> --- a/arch/riscv/cpu/cpu.c
> +++ b/arch/riscv/cpu/cpu.c
> @@ -36,6 +36,7 @@ static inline bool supports_extension(char ext)
>  #ifdef CONFIG_CPU
>         struct udevice *dev;
>         char desc[32];
> +       int i;
> 
>         uclass_find_first_device(UCLASS_CPU, &dev);
>         if (!dev) {
> @@ -43,9 +44,16 @@ static inline bool supports_extension(char ext)
>                 return false;
>         }
>         if (!cpu_get_desc(dev, desc, sizeof(desc))) {
> -               /* skip the first 4 characters (rv32|rv64) */
> -               if (strchr(desc + 4, ext))
> -                       return true;
> +               /*
> +                * skip the first 4 characters (rv32|rv64) and
> +                * check until underscore
> +                */
> +               for (i = 4; i < sizeof(desc); i++) {
> +                       if (desc[i] == '_' || desc[i] == '\0')
> +                               break;
> +                       if (desc[i] == ext)
> +                               return true;
> +               }
> 

Reviewed-by: Padmarao Begari <padmarao.begari@microchip.com>

>         }
> 
>         return false;
> --
> 2.34.1
> 

Re: [PATCH v2] riscv: Fix detecting FPU support in standard extension

[Samuel Holland]

On 11/5/22 01:02, Yu Chien Peter Lin wrote:
> We should check the string until it hits underscore, in case it
> searches for the letters in the custom extension. For example,
> "rv64imac_xandes" will be treated as D extension support since
> there is a "d" in "andes", resulting illegal instruction caused
> by initializing FCSR.
> 
> Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
> ---
>  arch/riscv/cpu/cpu.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
> index 52ab02519f..d34c8efce0 100644
> --- a/arch/riscv/cpu/cpu.c
> +++ b/arch/riscv/cpu/cpu.c
> @@ -36,6 +36,7 @@ static inline bool supports_extension(char ext)
>  #ifdef CONFIG_CPU
>  	struct udevice *dev;
>  	char desc[32];
> +	int i;
>  
>  	uclass_find_first_device(UCLASS_CPU, &dev);
>  	if (!dev) {
> @@ -43,9 +44,16 @@ static inline bool supports_extension(char ext)
>  		return false;
>  	}
>  	if (!cpu_get_desc(dev, desc, sizeof(desc))) {
> -		/* skip the first 4 characters (rv32|rv64) */
> -		if (strchr(desc + 4, ext))
> -			return true;
> +		/*
> +		 * skip the first 4 characters (rv32|rv64) and
> +		 * check until underscore
> +		 */

This probably works for the intended usage, but it is not guaranteed to
work. Underscores are allowed even between single-letter extensions. See
section 29.5 ("Underscores") of the unprivileged spec. Still, this is an
improvement, so:

Reviewed-by: Samuel Holland <samuel@sholland.org>

> +		for (i = 4; i < sizeof(desc); i++) {
> +			if (desc[i] == '_' || desc[i] == '\0')
> +				break;
> +			if (desc[i] == ext)
> +				return true;
> +		}
>  	}
>  
>  	return false;

Re: [PATCH v2] riscv: Fix detecting FPU support in standard extension

[Yu-Chien Peter Lin]

On Sun, Nov 13, 2022 at 03:47:38PM -0600, Samuel Holland wrote:
> On 11/5/22 01:02, Yu Chien Peter Lin wrote:
> > We should check the string until it hits underscore, in case it
> > searches for the letters in the custom extension. For example,
> > "rv64imac_xandes" will be treated as D extension support since
> > there is a "d" in "andes", resulting illegal instruction caused
> > by initializing FCSR.
> > 
> > Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
> > ---
> >  arch/riscv/cpu/cpu.c | 14 +++++++++++---
> >  1 file changed, 11 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
> > index 52ab02519f..d34c8efce0 100644
> > --- a/arch/riscv/cpu/cpu.c
> > +++ b/arch/riscv/cpu/cpu.c
> > @@ -36,6 +36,7 @@ static inline bool supports_extension(char ext)
> >  #ifdef CONFIG_CPU
> >  	struct udevice *dev;
> >  	char desc[32];
> > +	int i;
> >  
> >  	uclass_find_first_device(UCLASS_CPU, &dev);
> >  	if (!dev) {
> > @@ -43,9 +44,16 @@ static inline bool supports_extension(char ext)
> >  		return false;
> >  	}
> >  	if (!cpu_get_desc(dev, desc, sizeof(desc))) {
> > -		/* skip the first 4 characters (rv32|rv64) */
> > -		if (strchr(desc + 4, ext))
> > -			return true;
> > +		/*
> > +		 * skip the first 4 characters (rv32|rv64) and
> > +		 * check until underscore
> > +		 */
> 
> This probably works for the intended usage, but it is not guaranteed to
> work. Underscores are allowed even between single-letter extensions. See
> section 29.5 ("Underscores") of the unprivileged spec. Still, this is an
> improvement, so:
> 
> Reviewed-by: Samuel Holland <samuel@sholland.org>

Aah, I missed that case.
I supposed the strings always match the pattern stated in riscv cpus
binding [1], the detection logic here needs to be updated once the
case is also allowed.

[1] https://github.com/torvalds/linux/blob/v6.1-rc5/Documentation/devicetree/bindings/riscv/cpus.yaml#L83

Thanks for your review!

Best regards,
Peter Lin

> 
> > +		for (i = 4; i < sizeof(desc); i++) {
> > +			if (desc[i] == '_' || desc[i] == '\0')
> > +				break;
> > +			if (desc[i] == ext)
> > +				return true;
> > +		}
> >  	}
> >  
> >  	return false;
>