[PATCH 0/2] riscv: Add macro for multiple nop instructions

[PATCH 0/2] riscv: Add macro for multiple nop instructions

[Heiko Stuebner]

Some cases need multiple nop instructions and arm64 already has a
nice helper for not needing to write all of them out but instead
use a helper to add n nops.

So add a similar thing to riscv and convert the T-Head PMA
alternative to use it.


Heiko Stuebner (2):
  riscv: introduce nops and __nops macros for NOP sequences
  riscv: convert the t-head pbmt errata to use the __nops macro

 arch/riscv/include/asm/asm.h         | 15 +++++++++++++++
 arch/riscv/include/asm/barrier.h     |  2 ++
 arch/riscv/include/asm/errata_list.h |  8 +-------
 3 files changed, 18 insertions(+), 7 deletions(-)

-- 
2.35.1


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[PATCH 1/2] riscv: introduce nops and __nops macros for NOP sequences

[Heiko Stuebner]

NOP sequences tend to get used for padding out alternative sections

This change adds macros for generating these sequences as both inline
asm blocks, but also as strings suitable for embedding in other asm
blocks directly.

It essentially mimics similar functionality from arm64 introduced by
Wil Deacon in commit f99a250cb6a3 ("arm64: barriers: introduce nops
and __nops macros for NOP sequences").

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
 arch/riscv/include/asm/asm.h     | 15 +++++++++++++++
 arch/riscv/include/asm/barrier.h |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
index 618d7c5af1a2..1b471ff73178 100644
--- a/arch/riscv/include/asm/asm.h
+++ b/arch/riscv/include/asm/asm.h
@@ -67,4 +67,19 @@
 #error "Unexpected __SIZEOF_SHORT__"
 #endif
 
+#ifdef __ASSEMBLY__
+
+/* Common assembly source macros */
+
+/*
+ * NOP sequence
+ */
+.macro	nops, num
+	.rept	\num
+	nop
+	.endr
+.endm
+
+#endif /* __ASSEMBLY__ */
+
 #endif /* _ASM_RISCV_ASM_H */
diff --git a/arch/riscv/include/asm/barrier.h b/arch/riscv/include/asm/barrier.h
index d0e24aaa2aa0..110752594228 100644
--- a/arch/riscv/include/asm/barrier.h
+++ b/arch/riscv/include/asm/barrier.h
@@ -13,6 +13,8 @@
 #ifndef __ASSEMBLY__
 
 #define nop()		__asm__ __volatile__ ("nop")
+#define __nops(n)	".rept	" #n "\nnop\n.endr\n"
+#define nops(n)		__asm__ __volatile__ (__nops(n))
 
 #define RISCV_FENCE(p, s) \
 	__asm__ __volatile__ ("fence " #p "," #s : : : "memory")
-- 
2.35.1


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[PATCH 2/2] riscv: convert the t-head pbmt errata to use the __nops macro

[Heiko Stuebner]

Instead of manually inserting the list of nops, use the recently
introduced __nops(n) macro to make everything more readable.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
 arch/riscv/include/asm/errata_list.h | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
index 416ead0f9a65..398e351e7002 100644
--- a/arch/riscv/include/asm/errata_list.h
+++ b/arch/riscv/include/asm/errata_list.h
@@ -68,13 +68,7 @@ asm(ALTERNATIVE_2("li %0, 0\t\nnop",					\
  */
 #define ALT_THEAD_PMA(_val)						\
 asm volatile(ALTERNATIVE(						\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop",								\
+	__nops(7),							\
 	"li      t3, %1\n\t"						\
 	"slli    t3, t3, %3\n\t"					\
 	"and     t3, %0, t3\n\t"					\
-- 
2.35.1


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Re: [PATCH 0/2] riscv: Add macro for multiple nop instructions

[Guo Ren]

Just a safe good coding convention point.

Reviewed-by: Guo Ren <guoren@kernel.org>

On Tue, Jun 7, 2022 at 10:31 PM Heiko Stuebner <heiko@sntech.de> wrote:
>
> Some cases need multiple nop instructions and arm64 already has a
> nice helper for not needing to write all of them out but instead
> use a helper to add n nops.
>
> So add a similar thing to riscv and convert the T-Head PMA
> alternative to use it.
>
>
> Heiko Stuebner (2):
>   riscv: introduce nops and __nops macros for NOP sequences
>   riscv: convert the t-head pbmt errata to use the __nops macro
>
>  arch/riscv/include/asm/asm.h         | 15 +++++++++++++++
>  arch/riscv/include/asm/barrier.h     |  2 ++
>  arch/riscv/include/asm/errata_list.h |  8 +-------
>  3 files changed, 18 insertions(+), 7 deletions(-)
>
> --
> 2.35.1
>


-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/

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Re: [PATCH 0/2] riscv: Add macro for multiple nop instructions

[Palmer Dabbelt]

On Tue, 07 Jun 2022 07:30:57 PDT (-0700), heiko@sntech.de wrote:
> Some cases need multiple nop instructions and arm64 already has a
> nice helper for not needing to write all of them out but instead
> use a helper to add n nops.
>
> So add a similar thing to riscv and convert the T-Head PMA
> alternative to use it.
>
>
> Heiko Stuebner (2):
>   riscv: introduce nops and __nops macros for NOP sequences
>   riscv: convert the t-head pbmt errata to use the __nops macro
>
>  arch/riscv/include/asm/asm.h         | 15 +++++++++++++++
>  arch/riscv/include/asm/barrier.h     |  2 ++
>  arch/riscv/include/asm/errata_list.h |  8 +-------
>  3 files changed, 18 insertions(+), 7 deletions(-)

Thanks, these are on for-next.  I had to fix up some minor conflicts, but
hopefuly nothing went wrong.

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Re: [PATCH 0/2] riscv: Add macro for multiple nop instructions

[Samuel Holland]

Hi Palmer,

On 7/21/22 9:16 PM, Palmer Dabbelt wrote:
> On Tue, 07 Jun 2022 07:30:57 PDT (-0700), heiko@sntech.de wrote:
>> Some cases need multiple nop instructions and arm64 already has a
>> nice helper for not needing to write all of them out but instead
>> use a helper to add n nops.
>>
>> So add a similar thing to riscv and convert the T-Head PMA
>> alternative to use it.
>>
>>
>> Heiko Stuebner (2):
>>   riscv: introduce nops and __nops macros for NOP sequences
>>   riscv: convert the t-head pbmt errata to use the __nops macro
>>
>>  arch/riscv/include/asm/asm.h         | 15 +++++++++++++++
>>  arch/riscv/include/asm/barrier.h     |  2 ++
>>  arch/riscv/include/asm/errata_list.h |  8 +-------
>>  3 files changed, 18 insertions(+), 7 deletions(-)
> 
> Thanks, these are on for-next.  I had to fix up some minor conflicts, but
> hopefuly nothing went wrong.

The conflicts are because the patch was sent on top of fixes, specifically
e83031564137 ("riscv: Fix ALT_THEAD_PMA's asm parameters"). Since you applied
this patch without pulling fixes in to for-next, now for-next conflicts with master.

Regards,
Samuel

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