[PATCH v4 0/2] RISC-V: clarify what some RISCV_ISA* config options do & redo Zbb toolchain dependency

[PATCH v4 0/2] RISC-V: clarify what some RISCV_ISA* config options do & redo Zbb toolchain dependency

[Conor Dooley]

From: Conor Dooley <conor.dooley@microchip.com>

Since one depends on the other, albeit trivially, here's a v4 of the Zbb
toolchain dep removal alongside the rewording of Kconfig options I'd
sent out before the merge window. I think I like this implementation
better than v1, but I couldn't think of a good name for a "public"
version of __ALTERNATIVE(), so I used it here directly.
Unfortunately "ALTERNATIVE_2_CFG" already exists and I couldn't think of
a good way to name an alternative macro that allows for several config
options that didn't make the distinction sufficiently clear.. Yell
if you have better suggestions than I did.

I am a wee bit "worried" that this makes the Kconfig option confusing as
it isn't immediately obvious if someone is or is not going to get the
toolchain based optimisations.

Cheers,
Conor.

v4:
- rebase since it's been a few months
- change some wording Alex wasn't fond of in patch 1
- remove a left over CONFIG_RISCV_ISA_ZBB_ALT from the v1 implementation
  in patch 2

CC: xiao.w.wang@intel.com
CC: Andrew Jones <ajones@ventanamicro.com>
CC: pulehui@huawei.com
CC: Charlie Jenkins <charlie@rivosinc.com>
CC: Paul Walmsley <paul.walmsley@sifive.com>
CC: Palmer Dabbelt <palmer@dabbelt.com>
CC: Conor Dooley <conor.dooley@microchip.com>
CC: linux-riscv@lists.infradead.org
CC: linux-kernel@vger.kernel.org
CC: Samuel Holland <samuel.holland@sifive.com>
CC: Pu Lehui <pulehui@huaweicloud.com>
CC: Björn Töpel <bjorn@kernel.org>
CC: Andrew Jones <ajones@ventanamicro.com>
CC: Paul Walmsley <paul.walmsley@sifive.com>
CC: Palmer Dabbelt <palmer@dabbelt.com>
CC: linux-riscv@lists.infradead.org

Conor Dooley (2):
  RISC-V: clarify what some RISCV_ISA* config options do
  RISC-V: separate Zbb optimisations requiring and not requiring
    toolchain support

 arch/riscv/Kconfig                    | 38 ++++++++++++++-------------
 arch/riscv/include/asm/arch_hweight.h |  6 ++---
 arch/riscv/include/asm/bitops.h       |  4 +--
 arch/riscv/include/asm/checksum.h     |  3 +--
 arch/riscv/lib/csum.c                 | 21 +++------------
 arch/riscv/lib/strcmp.S               |  5 ++--
 arch/riscv/lib/strlen.S               |  5 ++--
 arch/riscv/lib/strncmp.S              |  5 ++--
 8 files changed, 38 insertions(+), 49 deletions(-)

-- 
2.45.2

[PATCH v4 1/2] RISC-V: clarify what some RISCV_ISA* config options do

[Conor Dooley]

From: Conor Dooley <conor.dooley@microchip.com>

During some discussion on IRC yesterday and on Pu's bpf patch [1]
I noticed that these RISCV_ISA* Kconfig options are not really clear
about their implications. Many of these options have no impact on what
userspace is allowed to do, for example an application can use Zbb
regardless of whether or not the kernel does. Change the help text to
try and clarify whether or not an option affects just the kernel, or
also userspace. None of these options actually control whether or not an
extension is detected dynamically as that's done regardless of Kconfig
options, so drop any text that implies the option is required for
dynamic detection, rewording them as "do x when y is detected".

Link: https://lore.kernel.org/linux-riscv/20240328-ferocity-repose-c554f75a676c@spud/ [1]
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
 arch/riscv/Kconfig | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 62545946ecf43..278a38c94c5a6 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -527,7 +527,8 @@ config RISCV_ISA_C
 	help
 	  Adds "C" to the ISA subsets that the toolchain is allowed to emit
 	  when building Linux, which results in compressed instructions in the
-	  Linux binary.
+	  Linux binary. This option produces a kernel that will not run on
+	  systems that do not support compressed instructions.
 
 	  If you don't know what to do here, say Y.
 
@@ -537,8 +538,8 @@ config RISCV_ISA_SVNAPOT
 	depends on RISCV_ALTERNATIVE
 	default y
 	help
-	  Allow kernel to detect the Svnapot ISA-extension dynamically at boot
-	  time and enable its usage.
+	  Enable support for the Svnapot ISA-extension when it is detected
+	  at boot.
 
 	  The Svnapot extension is used to mark contiguous PTEs as a range
 	  of contiguous virtual-to-physical translations for a naturally
@@ -556,9 +557,8 @@ config RISCV_ISA_SVPBMT
 	depends on RISCV_ALTERNATIVE
 	default y
 	help
-	   Adds support to dynamically detect the presence of the Svpbmt
-	   ISA-extension (Supervisor-mode: page-based memory types) and
-	   enable its usage.
+	   Add support for the Svpbmt ISA-extension (Supervisor-mode:
+	   page-based memory types) in the kernel when it is detected at boot.
 
 	   The memory type for a page contains a combination of attributes
 	   that indicate the cacheability, idempotency, and ordering
@@ -577,14 +577,15 @@ config TOOLCHAIN_HAS_V
 	depends on AS_HAS_OPTION_ARCH
 
 config RISCV_ISA_V
-	bool "VECTOR extension support"
+	bool "Vector extension support"
 	depends on TOOLCHAIN_HAS_V
 	depends on FPU
 	select DYNAMIC_SIGFRAME
 	default y
 	help
-	  Say N here if you want to disable all vector related procedure
-	  in the kernel.
+	  Add support for the Vector extension when it is detected at boot.
+	  When this option is disabled, neither the kernel nor userspace may
+	  use vector procedures.
 
 	  If you don't know what to do here, say Y.
 
@@ -667,8 +668,8 @@ config RISCV_ISA_ZBB
 	depends on RISCV_ALTERNATIVE
 	default y
 	help
-	   Adds support to dynamically detect the presence of the ZBB
-	   extension (basic bit manipulation) and enable its usage.
+	   Add support for enabling optimisations in the kernel when the
+	   Zbb extension is detected at boot.
 
 	   The Zbb extension provides instructions to accelerate a number
 	   of bit-specific operations (count bit population, sign extending,
@@ -707,9 +708,9 @@ config RISCV_ISA_ZICBOM
 	select RISCV_DMA_NONCOHERENT
 	select DMA_DIRECT_REMAP
 	help
-	   Adds support to dynamically detect the presence of the ZICBOM
-	   extension (Cache Block Management Operations) and enable its
-	   usage.
+	   Add support for the Zicbom extension (Cache Block Management
+	   Operations) and enable its use in the kernel when it is detected
+	   at boot.
 
 	   The Zicbom extension can be used to handle for example
 	   non-coherent DMA support on devices that need it.
@@ -722,7 +723,7 @@ config RISCV_ISA_ZICBOZ
 	default y
 	help
 	   Enable the use of the Zicboz extension (cbo.zero instruction)
-	   when available.
+	   in the kernel when it is detected at boot.
 
 	   The Zicboz extension is used for faster zeroing of memory.
 
@@ -760,8 +761,9 @@ config FPU
 	bool "FPU support"
 	default y
 	help
-	  Say N here if you want to disable all floating-point related procedure
-	  in the kernel.
+	  Add support for floating point operations when an FPU is detected at
+	  boot. When this option is disabled, neither the kernel nor userspace
+	  may use the floating point unit.
 
 	  If you don't know what to do here, say Y.
 
-- 
2.45.2

[PATCH v4 2/2] RISC-V: separate Zbb optimisations requiring and not requiring toolchain support

[Conor Dooley]

From: Conor Dooley <conor.dooley@microchip.com>

It seems a bit ridiculous to require toolchain support for BPF to
assemble Zbb instructions, so move the dependency on toolchain support
for Zbb optimisations out of the Kconfig option and to the callsites.

Zbb support has always depended on alternatives, so while adjusting the
config options guarding optimisations, remove any checks for
whether or not alternatives are enabled.

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
 arch/riscv/Kconfig                    |  4 ++--
 arch/riscv/include/asm/arch_hweight.h |  6 +++---
 arch/riscv/include/asm/bitops.h       |  4 ++--
 arch/riscv/include/asm/checksum.h     |  3 +--
 arch/riscv/lib/csum.c                 | 21 +++------------------
 arch/riscv/lib/strcmp.S               |  5 +++--
 arch/riscv/lib/strlen.S               |  5 +++--
 arch/riscv/lib/strncmp.S              |  5 +++--
 8 files changed, 20 insertions(+), 33 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 278a38c94c5a6..6ec7a500a25ff 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -664,12 +664,12 @@ config RISCV_ISA_ZBA
 
 config RISCV_ISA_ZBB
 	bool "Zbb extension support for bit manipulation instructions"
-	depends on TOOLCHAIN_HAS_ZBB
 	depends on RISCV_ALTERNATIVE
 	default y
 	help
 	   Add support for enabling optimisations in the kernel when the
-	   Zbb extension is detected at boot.
+	   Zbb extension is detected at boot. Some optimisations may
+	   additionally depend on toolchain support for Zbb.
 
 	   The Zbb extension provides instructions to accelerate a number
 	   of bit-specific operations (count bit population, sign extending,
diff --git a/arch/riscv/include/asm/arch_hweight.h b/arch/riscv/include/asm/arch_hweight.h
index 613769b9cdc90..0e7cdbbec8efd 100644
--- a/arch/riscv/include/asm/arch_hweight.h
+++ b/arch/riscv/include/asm/arch_hweight.h
@@ -19,7 +19,7 @@
 
 static __always_inline unsigned int __arch_hweight32(unsigned int w)
 {
-#ifdef CONFIG_RISCV_ISA_ZBB
+#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
 	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
 				      RISCV_ISA_EXT_ZBB, 1)
 			  : : : : legacy);
@@ -50,7 +50,7 @@ static inline unsigned int __arch_hweight8(unsigned int w)
 #if BITS_PER_LONG == 64
 static __always_inline unsigned long __arch_hweight64(__u64 w)
 {
-# ifdef CONFIG_RISCV_ISA_ZBB
+#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
 	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
 				      RISCV_ISA_EXT_ZBB, 1)
 			  : : : : legacy);
@@ -64,7 +64,7 @@ static __always_inline unsigned long __arch_hweight64(__u64 w)
 	return w;
 
 legacy:
-# endif
+#endif
 	return __sw_hweight64(w);
 }
 #else /* BITS_PER_LONG == 64 */
diff --git a/arch/riscv/include/asm/bitops.h b/arch/riscv/include/asm/bitops.h
index fae152ea0508d..410e2235d6589 100644
--- a/arch/riscv/include/asm/bitops.h
+++ b/arch/riscv/include/asm/bitops.h
@@ -15,7 +15,7 @@
 #include <asm/barrier.h>
 #include <asm/bitsperlong.h>
 
-#if !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE)
+#if !(defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)) || defined(NO_ALTERNATIVE)
 #include <asm-generic/bitops/__ffs.h>
 #include <asm-generic/bitops/__fls.h>
 #include <asm-generic/bitops/ffs.h>
@@ -175,7 +175,7 @@ static __always_inline int variable_fls(unsigned int x)
 	 variable_fls(x_);					\
 })
 
-#endif /* !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE) */
+#endif /* !(defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)) || defined(NO_ALTERNATIVE) */
 
 #include <asm-generic/bitops/ffz.h>
 #include <asm-generic/bitops/fls64.h>
diff --git a/arch/riscv/include/asm/checksum.h b/arch/riscv/include/asm/checksum.h
index 88e6f1499e889..da378856f1d59 100644
--- a/arch/riscv/include/asm/checksum.h
+++ b/arch/riscv/include/asm/checksum.h
@@ -49,8 +49,7 @@ static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
 	 * ZBB only saves three instructions on 32-bit and five on 64-bit so not
 	 * worth checking if supported without Alternatives.
 	 */
-	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
-	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
 		unsigned long fold_temp;
 
 		asm goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
index 7fb12c59e5719..9408f50ca59a8 100644
--- a/arch/riscv/lib/csum.c
+++ b/arch/riscv/lib/csum.c
@@ -40,12 +40,7 @@ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
 	uproto = (__force unsigned int)htonl(proto);
 	sum += uproto;
 
-	/*
-	 * Zbb support saves 4 instructions, so not worth checking without
-	 * alternatives if supported
-	 */
-	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
-	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
 		unsigned long fold_temp;
 
 		/*
@@ -157,12 +152,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
 	csum = do_csum_common(ptr, end, data);
 
 #ifdef CC_HAS_ASM_GOTO_TIED_OUTPUT
-	/*
-	 * Zbb support saves 6 instructions, so not worth checking without
-	 * alternatives if supported
-	 */
-	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
-	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
 		unsigned long fold_temp;
 
 		/*
@@ -244,12 +234,7 @@ do_csum_no_alignment(const unsigned char *buff, int len)
 	end = (const unsigned long *)(buff + len);
 	csum = do_csum_common(ptr, end, data);
 
-	/*
-	 * Zbb support saves 6 instructions, so not worth checking without
-	 * alternatives if supported
-	 */
-	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
-	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
 		unsigned long fold_temp;
 
 		/*
diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S
index 57a5c00662315..65027e742af15 100644
--- a/arch/riscv/lib/strcmp.S
+++ b/arch/riscv/lib/strcmp.S
@@ -8,7 +8,8 @@
 /* int strcmp(const char *cs, const char *ct) */
 SYM_FUNC_START(strcmp)
 
-	ALTERNATIVE("nop", "j strcmp_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB)
+	__ALTERNATIVE_CFG("nop", "j strcmp_zbb", 0, RISCV_ISA_EXT_ZBB,
+		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
 
 	/*
 	 * Returns
@@ -43,7 +44,7 @@ SYM_FUNC_START(strcmp)
  * The code was published as part of the bitmanip manual
  * in Appendix A.
  */
-#ifdef CONFIG_RISCV_ISA_ZBB
+#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
 strcmp_zbb:
 
 .option push
diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
index 962983b73251e..eb4d2b7ed22b6 100644
--- a/arch/riscv/lib/strlen.S
+++ b/arch/riscv/lib/strlen.S
@@ -8,7 +8,8 @@
 /* int strlen(const char *s) */
 SYM_FUNC_START(strlen)
 
-	ALTERNATIVE("nop", "j strlen_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB)
+	__ALTERNATIVE_CFG("nop", "j strlen_zbb", 0, RISCV_ISA_EXT_ZBB,
+		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
 
 	/*
 	 * Returns
@@ -33,7 +34,7 @@ SYM_FUNC_START(strlen)
 /*
  * Variant of strlen using the ZBB extension if available
  */
-#ifdef CONFIG_RISCV_ISA_ZBB
+#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
 strlen_zbb:
 
 #ifdef CONFIG_CPU_BIG_ENDIAN
diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S
index 7b2d0ff9ed6c7..062000c468c83 100644
--- a/arch/riscv/lib/strncmp.S
+++ b/arch/riscv/lib/strncmp.S
@@ -8,7 +8,8 @@
 /* int strncmp(const char *cs, const char *ct, size_t count) */
 SYM_FUNC_START(strncmp)
 
-	ALTERNATIVE("nop", "j strncmp_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB)
+	__ALTERNATIVE_CFG("nop", "j strncmp_zbb", 0, RISCV_ISA_EXT_ZBB,
+		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
 
 	/*
 	 * Returns
@@ -46,7 +47,7 @@ SYM_FUNC_START(strncmp)
 /*
  * Variant of strncmp using the ZBB extension if available
  */
-#ifdef CONFIG_RISCV_ISA_ZBB
+#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
 strncmp_zbb:
 
 .option push
-- 
2.45.2

Re: [PATCH v4 1/2] RISC-V: clarify what some RISCV_ISA* config options do

[Samuel Holland]

On 2024-10-24 5:19 AM, Conor Dooley wrote:
> From: Conor Dooley <conor.dooley@microchip.com>
> 
> During some discussion on IRC yesterday and on Pu's bpf patch [1]
> I noticed that these RISCV_ISA* Kconfig options are not really clear
> about their implications. Many of these options have no impact on what
> userspace is allowed to do, for example an application can use Zbb
> regardless of whether or not the kernel does. Change the help text to
> try and clarify whether or not an option affects just the kernel, or
> also userspace. None of these options actually control whether or not an
> extension is detected dynamically as that's done regardless of Kconfig
> options, so drop any text that implies the option is required for
> dynamic detection, rewording them as "do x when y is detected".
> 
> Link: https://lore.kernel.org/linux-riscv/20240328-ferocity-repose-c554f75a676c@spud/ [1]
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
>  arch/riscv/Kconfig | 36 +++++++++++++++++++-----------------
>  1 file changed, 19 insertions(+), 17 deletions(-)

Reviewed-by: Samuel Holland <samuel.holland@sifive.com>

Re: [PATCH v4 2/2] RISC-V: separate Zbb optimisations requiring and not requiring toolchain support

[Samuel Holland]

On 2024-10-24 5:19 AM, Conor Dooley wrote:
> From: Conor Dooley <conor.dooley@microchip.com>
> 
> It seems a bit ridiculous to require toolchain support for BPF to
> assemble Zbb instructions, so move the dependency on toolchain support
> for Zbb optimisations out of the Kconfig option and to the callsites.
> 
> Zbb support has always depended on alternatives, so while adjusting the
> config options guarding optimisations, remove any checks for
> whether or not alternatives are enabled.
> 
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
>  arch/riscv/Kconfig                    |  4 ++--
>  arch/riscv/include/asm/arch_hweight.h |  6 +++---
>  arch/riscv/include/asm/bitops.h       |  4 ++--
>  arch/riscv/include/asm/checksum.h     |  3 +--
>  arch/riscv/lib/csum.c                 | 21 +++------------------
>  arch/riscv/lib/strcmp.S               |  5 +++--
>  arch/riscv/lib/strlen.S               |  5 +++--
>  arch/riscv/lib/strncmp.S              |  5 +++--
>  8 files changed, 20 insertions(+), 33 deletions(-)

Reviewed-by: Samuel Holland <samuel.holland@sifive.com>

Re: [PATCH v4 1/2] RISC-V: clarify what some RISCV_ISA* config options do

[Charlie Jenkins]

On Thu, Oct 24, 2024 at 11:19:40AM +0100, Conor Dooley wrote:
> From: Conor Dooley <conor.dooley@microchip.com>
> 
> During some discussion on IRC yesterday and on Pu's bpf patch [1]
> I noticed that these RISCV_ISA* Kconfig options are not really clear
> about their implications. Many of these options have no impact on what
> userspace is allowed to do, for example an application can use Zbb
> regardless of whether or not the kernel does. Change the help text to
> try and clarify whether or not an option affects just the kernel, or
> also userspace. None of these options actually control whether or not an
> extension is detected dynamically as that's done regardless of Kconfig
> options, so drop any text that implies the option is required for
> dynamic detection, rewording them as "do x when y is detected".
> 
> Link: https://lore.kernel.org/linux-riscv/20240328-ferocity-repose-c554f75a676c@spud/ [1]
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

This has been sitting around for a while but is a good change.

Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>

> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
>  arch/riscv/Kconfig | 36 +++++++++++++++++++-----------------
>  1 file changed, 19 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 62545946ecf43..278a38c94c5a6 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -527,7 +527,8 @@ config RISCV_ISA_C
>  	help
>  	  Adds "C" to the ISA subsets that the toolchain is allowed to emit
>  	  when building Linux, which results in compressed instructions in the
> -	  Linux binary.
> +	  Linux binary. This option produces a kernel that will not run on
> +	  systems that do not support compressed instructions.
>  
>  	  If you don't know what to do here, say Y.
>  
> @@ -537,8 +538,8 @@ config RISCV_ISA_SVNAPOT
>  	depends on RISCV_ALTERNATIVE
>  	default y
>  	help
> -	  Allow kernel to detect the Svnapot ISA-extension dynamically at boot
> -	  time and enable its usage.
> +	  Enable support for the Svnapot ISA-extension when it is detected
> +	  at boot.
>  
>  	  The Svnapot extension is used to mark contiguous PTEs as a range
>  	  of contiguous virtual-to-physical translations for a naturally
> @@ -556,9 +557,8 @@ config RISCV_ISA_SVPBMT
>  	depends on RISCV_ALTERNATIVE
>  	default y
>  	help
> -	   Adds support to dynamically detect the presence of the Svpbmt
> -	   ISA-extension (Supervisor-mode: page-based memory types) and
> -	   enable its usage.
> +	   Add support for the Svpbmt ISA-extension (Supervisor-mode:
> +	   page-based memory types) in the kernel when it is detected at boot.
>  
>  	   The memory type for a page contains a combination of attributes
>  	   that indicate the cacheability, idempotency, and ordering
> @@ -577,14 +577,15 @@ config TOOLCHAIN_HAS_V
>  	depends on AS_HAS_OPTION_ARCH
>  
>  config RISCV_ISA_V
> -	bool "VECTOR extension support"
> +	bool "Vector extension support"
>  	depends on TOOLCHAIN_HAS_V
>  	depends on FPU
>  	select DYNAMIC_SIGFRAME
>  	default y
>  	help
> -	  Say N here if you want to disable all vector related procedure
> -	  in the kernel.
> +	  Add support for the Vector extension when it is detected at boot.
> +	  When this option is disabled, neither the kernel nor userspace may
> +	  use vector procedures.
>  
>  	  If you don't know what to do here, say Y.
>  
> @@ -667,8 +668,8 @@ config RISCV_ISA_ZBB
>  	depends on RISCV_ALTERNATIVE
>  	default y
>  	help
> -	   Adds support to dynamically detect the presence of the ZBB
> -	   extension (basic bit manipulation) and enable its usage.
> +	   Add support for enabling optimisations in the kernel when the
> +	   Zbb extension is detected at boot.
>  
>  	   The Zbb extension provides instructions to accelerate a number
>  	   of bit-specific operations (count bit population, sign extending,
> @@ -707,9 +708,9 @@ config RISCV_ISA_ZICBOM
>  	select RISCV_DMA_NONCOHERENT
>  	select DMA_DIRECT_REMAP
>  	help
> -	   Adds support to dynamically detect the presence of the ZICBOM
> -	   extension (Cache Block Management Operations) and enable its
> -	   usage.
> +	   Add support for the Zicbom extension (Cache Block Management
> +	   Operations) and enable its use in the kernel when it is detected
> +	   at boot.
>  
>  	   The Zicbom extension can be used to handle for example
>  	   non-coherent DMA support on devices that need it.
> @@ -722,7 +723,7 @@ config RISCV_ISA_ZICBOZ
>  	default y
>  	help
>  	   Enable the use of the Zicboz extension (cbo.zero instruction)
> -	   when available.
> +	   in the kernel when it is detected at boot.
>  
>  	   The Zicboz extension is used for faster zeroing of memory.
>  
> @@ -760,8 +761,9 @@ config FPU
>  	bool "FPU support"
>  	default y
>  	help
> -	  Say N here if you want to disable all floating-point related procedure
> -	  in the kernel.
> +	  Add support for floating point operations when an FPU is detected at
> +	  boot. When this option is disabled, neither the kernel nor userspace
> +	  may use the floating point unit.
>  
>  	  If you don't know what to do here, say Y.
>  
> -- 
> 2.45.2
> 

Re: [PATCH v4 2/2] RISC-V: separate Zbb optimisations requiring and not requiring toolchain support

[Charlie Jenkins]

On Thu, Oct 24, 2024 at 11:19:41AM +0100, Conor Dooley wrote:
> From: Conor Dooley <conor.dooley@microchip.com>
> 
> It seems a bit ridiculous to require toolchain support for BPF to
> assemble Zbb instructions, so move the dependency on toolchain support
> for Zbb optimisations out of the Kconfig option and to the callsites.
> 
> Zbb support has always depended on alternatives, so while adjusting the
> config options guarding optimisations, remove any checks for
> whether or not alternatives are enabled.
> 
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
>  arch/riscv/Kconfig                    |  4 ++--
>  arch/riscv/include/asm/arch_hweight.h |  6 +++---
>  arch/riscv/include/asm/bitops.h       |  4 ++--
>  arch/riscv/include/asm/checksum.h     |  3 +--
>  arch/riscv/lib/csum.c                 | 21 +++------------------
>  arch/riscv/lib/strcmp.S               |  5 +++--
>  arch/riscv/lib/strlen.S               |  5 +++--
>  arch/riscv/lib/strncmp.S              |  5 +++--
>  8 files changed, 20 insertions(+), 33 deletions(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 278a38c94c5a6..6ec7a500a25ff 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -664,12 +664,12 @@ config RISCV_ISA_ZBA
>  
>  config RISCV_ISA_ZBB
>  	bool "Zbb extension support for bit manipulation instructions"
> -	depends on TOOLCHAIN_HAS_ZBB
>  	depends on RISCV_ALTERNATIVE
>  	default y
>  	help
>  	   Add support for enabling optimisations in the kernel when the
> -	   Zbb extension is detected at boot.
> +	   Zbb extension is detected at boot. Some optimisations may
> +	   additionally depend on toolchain support for Zbb.
>  
>  	   The Zbb extension provides instructions to accelerate a number
>  	   of bit-specific operations (count bit population, sign extending,
> diff --git a/arch/riscv/include/asm/arch_hweight.h b/arch/riscv/include/asm/arch_hweight.h
> index 613769b9cdc90..0e7cdbbec8efd 100644
> --- a/arch/riscv/include/asm/arch_hweight.h
> +++ b/arch/riscv/include/asm/arch_hweight.h
> @@ -19,7 +19,7 @@
>  
>  static __always_inline unsigned int __arch_hweight32(unsigned int w)
>  {
> -#ifdef CONFIG_RISCV_ISA_ZBB
> +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
>  	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
>  				      RISCV_ISA_EXT_ZBB, 1)
>  			  : : : : legacy);
> @@ -50,7 +50,7 @@ static inline unsigned int __arch_hweight8(unsigned int w)
>  #if BITS_PER_LONG == 64
>  static __always_inline unsigned long __arch_hweight64(__u64 w)
>  {
> -# ifdef CONFIG_RISCV_ISA_ZBB
> +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
>  	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
>  				      RISCV_ISA_EXT_ZBB, 1)
>  			  : : : : legacy);
> @@ -64,7 +64,7 @@ static __always_inline unsigned long __arch_hweight64(__u64 w)
>  	return w;
>  
>  legacy:
> -# endif
> +#endif
>  	return __sw_hweight64(w);
>  }
>  #else /* BITS_PER_LONG == 64 */
> diff --git a/arch/riscv/include/asm/bitops.h b/arch/riscv/include/asm/bitops.h
> index fae152ea0508d..410e2235d6589 100644
> --- a/arch/riscv/include/asm/bitops.h
> +++ b/arch/riscv/include/asm/bitops.h
> @@ -15,7 +15,7 @@
>  #include <asm/barrier.h>
>  #include <asm/bitsperlong.h>
>  
> -#if !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE)
> +#if !(defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)) || defined(NO_ALTERNATIVE)
>  #include <asm-generic/bitops/__ffs.h>
>  #include <asm-generic/bitops/__fls.h>
>  #include <asm-generic/bitops/ffs.h>
> @@ -175,7 +175,7 @@ static __always_inline int variable_fls(unsigned int x)
>  	 variable_fls(x_);					\
>  })
>  
> -#endif /* !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE) */
> +#endif /* !(defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)) || defined(NO_ALTERNATIVE) */
>  
>  #include <asm-generic/bitops/ffz.h>
>  #include <asm-generic/bitops/fls64.h>
> diff --git a/arch/riscv/include/asm/checksum.h b/arch/riscv/include/asm/checksum.h
> index 88e6f1499e889..da378856f1d59 100644
> --- a/arch/riscv/include/asm/checksum.h
> +++ b/arch/riscv/include/asm/checksum.h
> @@ -49,8 +49,7 @@ static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
>  	 * ZBB only saves three instructions on 32-bit and five on 64-bit so not
>  	 * worth checking if supported without Alternatives.
>  	 */
> -	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> -	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
>  		unsigned long fold_temp;
>  
>  		asm goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
> diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
> index 7fb12c59e5719..9408f50ca59a8 100644
> --- a/arch/riscv/lib/csum.c
> +++ b/arch/riscv/lib/csum.c
> @@ -40,12 +40,7 @@ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
>  	uproto = (__force unsigned int)htonl(proto);
>  	sum += uproto;
>  
> -	/*
> -	 * Zbb support saves 4 instructions, so not worth checking without
> -	 * alternatives if supported
> -	 */
> -	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> -	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
>  		unsigned long fold_temp;
>  
>  		/*
> @@ -157,12 +152,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
>  	csum = do_csum_common(ptr, end, data);
>  
>  #ifdef CC_HAS_ASM_GOTO_TIED_OUTPUT
> -	/*
> -	 * Zbb support saves 6 instructions, so not worth checking without
> -	 * alternatives if supported
> -	 */
> -	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> -	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
>  		unsigned long fold_temp;
>  
>  		/*
> @@ -244,12 +234,7 @@ do_csum_no_alignment(const unsigned char *buff, int len)
>  	end = (const unsigned long *)(buff + len);
>  	csum = do_csum_common(ptr, end, data);
>  
> -	/*
> -	 * Zbb support saves 6 instructions, so not worth checking without
> -	 * alternatives if supported
> -	 */
> -	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
> -	    IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> +	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
>  		unsigned long fold_temp;
>  
>  		/*
> diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S
> index 57a5c00662315..65027e742af15 100644
> --- a/arch/riscv/lib/strcmp.S
> +++ b/arch/riscv/lib/strcmp.S
> @@ -8,7 +8,8 @@
>  /* int strcmp(const char *cs, const char *ct) */
>  SYM_FUNC_START(strcmp)
>  
> -	ALTERNATIVE("nop", "j strcmp_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB)
> +	__ALTERNATIVE_CFG("nop", "j strcmp_zbb", 0, RISCV_ISA_EXT_ZBB,
> +		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
>  
>  	/*
>  	 * Returns
> @@ -43,7 +44,7 @@ SYM_FUNC_START(strcmp)
>   * The code was published as part of the bitmanip manual
>   * in Appendix A.
>   */
> -#ifdef CONFIG_RISCV_ISA_ZBB
> +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
>  strcmp_zbb:
>  
>  .option push
> diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
> index 962983b73251e..eb4d2b7ed22b6 100644
> --- a/arch/riscv/lib/strlen.S
> +++ b/arch/riscv/lib/strlen.S
> @@ -8,7 +8,8 @@
>  /* int strlen(const char *s) */
>  SYM_FUNC_START(strlen)
>  
> -	ALTERNATIVE("nop", "j strlen_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB)
> +	__ALTERNATIVE_CFG("nop", "j strlen_zbb", 0, RISCV_ISA_EXT_ZBB,
> +		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
>  
>  	/*
>  	 * Returns
> @@ -33,7 +34,7 @@ SYM_FUNC_START(strlen)
>  /*
>   * Variant of strlen using the ZBB extension if available
>   */
> -#ifdef CONFIG_RISCV_ISA_ZBB
> +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
>  strlen_zbb:
>  
>  #ifdef CONFIG_CPU_BIG_ENDIAN
> diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S
> index 7b2d0ff9ed6c7..062000c468c83 100644
> --- a/arch/riscv/lib/strncmp.S
> +++ b/arch/riscv/lib/strncmp.S
> @@ -8,7 +8,8 @@
>  /* int strncmp(const char *cs, const char *ct, size_t count) */
>  SYM_FUNC_START(strncmp)
>  
> -	ALTERNATIVE("nop", "j strncmp_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB)
> +	__ALTERNATIVE_CFG("nop", "j strncmp_zbb", 0, RISCV_ISA_EXT_ZBB,
> +		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
>  
>  	/*
>  	 * Returns
> @@ -46,7 +47,7 @@ SYM_FUNC_START(strncmp)
>  /*
>   * Variant of strncmp using the ZBB extension if available
>   */
> -#ifdef CONFIG_RISCV_ISA_ZBB
> +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
>  strncmp_zbb:
>  
>  .option push
> -- 
> 2.45.2
> 

Re: [PATCH v4 0/2] RISC-V: clarify what some RISCV_ISA* config options do & redo Zbb toolchain dependency

[patchwork-bot+linux-riscv]

Hello:

This series was applied to riscv/linux.git (for-next)
by Alexandre Ghiti <alexghiti@rivosinc.com>:

On Thu, 24 Oct 2024 11:19:39 +0100 you wrote:
> From: Conor Dooley <conor.dooley@microchip.com>
> 
> Since one depends on the other, albeit trivially, here's a v4 of the Zbb
> toolchain dep removal alongside the rewording of Kconfig options I'd
> sent out before the merge window. I think I like this implementation
> better than v1, but I couldn't think of a good name for a "public"
> version of __ALTERNATIVE(), so I used it here directly.
> Unfortunately "ALTERNATIVE_2_CFG" already exists and I couldn't think of
> a good way to name an alternative macro that allows for several config
> options that didn't make the distinction sufficiently clear.. Yell
> if you have better suggestions than I did.
> 
> [...]

Here is the summary with links:
  - [v4,1/2] RISC-V: clarify what some RISCV_ISA* config options do
    https://git.kernel.org/riscv/c/6216182fb776
  - [v4,2/2] RISC-V: separate Zbb optimisations requiring and not requiring toolchain support
    https://git.kernel.org/riscv/c/9343aaba1f25

You are awesome, thank you!
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