[PATCH] RISC-V: Remove udivdi3

[PATCH] RISC-V: Remove udivdi3

[Palmer Dabbelt]

This should never have landed in the first place: it was added as part
of 64-bit divide support for 32-bit systems, but the kernel doesn't
allow this sort of division.  I must have forgotten to remove it.

This patch removes the support.  Since this routine only worked on
64-bit platforms but was only built on 32-bit platforms, it's
essentially just nonsense anyway.

Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
---
 arch/riscv/lib/Makefile  |  2 --
 arch/riscv/lib/udivdi3.S | 32 --------------------------------
 2 files changed, 34 deletions(-)
 delete mode 100644 arch/riscv/lib/udivdi3.S

diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 8e364ebf37de..267feaa10f6a 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -5,5 +5,3 @@ lib-y	+= memset.o
 lib-y	+= uaccess.o
 
 lib-$(CONFIG_64BIT) += tishift.o
-
-lib-$(CONFIG_32BIT) += udivdi3.o
diff --git a/arch/riscv/lib/udivdi3.S b/arch/riscv/lib/udivdi3.S
deleted file mode 100644
index 3f07476a91a9..000000000000
--- a/arch/riscv/lib/udivdi3.S
+++ /dev/null
@@ -1,32 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Copyright (C) 2016-2017 Free Software Foundation, Inc.
- */
-
-#include <linux/linkage.h>
-
-ENTRY(__udivdi3)
-	mv	a2, a1
-	mv	a1, a0
-	li	a0, -1
-	beqz	a2, .L5
-	li	a3, 1
-	bgeu	a2, a1, .L2
-.L1:
-	blez	a2, .L2
-	slli	a2, a2, 1
-	slli	a3, a3, 1
-	bgtu	a1, a2, .L1
-.L2:
-	li	a0, 0
-.L3:
-	bltu	a1, a2, .L4
-	sub	a1, a1, a2
-	or	a0, a0, a3
-.L4:
-	srli	a3, a3, 1
-	srli	a2, a2, 1
-	bnez	a3, .L3
-.L5:
-	ret
-ENDPROC(__udivdi3)
-- 
2.21.0


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Re: [PATCH] RISC-V: Remove udivdi3

[Alan Kao]

On Tue, Aug 06, 2019 at 05:05:08PM -0700, Palmer Dabbelt wrote:
> This should never have landed in the first place: it was added as part
> of 64-bit divide support for 32-bit systems, but the kernel doesn't
> allow this sort of division.  I must have forgotten to remove it.
> 
> This patch removes the support.  Since this routine only worked on
> 64-bit platforms but was only built on 32-bit platforms, it's
> essentially just nonsense anyway.
> 

It would be more complete if we add
"Reported-by: Eric Lin <tesheng@andestech.com>" here.

> Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
> Acked-by: Nicolas Pitre <nico@fluxnic.net>
> ---
>  arch/riscv/lib/Makefile  |  2 --
>  arch/riscv/lib/udivdi3.S | 32 --------------------------------
>  2 files changed, 34 deletions(-)
>  delete mode 100644 arch/riscv/lib/udivdi3.S
> 
> diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
> index 8e364ebf37de..267feaa10f6a 100644
> --- a/arch/riscv/lib/Makefile
> +++ b/arch/riscv/lib/Makefile
> @@ -5,5 +5,3 @@ lib-y	+= memset.o
>  lib-y	+= uaccess.o
>  
>  lib-$(CONFIG_64BIT) += tishift.o
> -
> -lib-$(CONFIG_32BIT) += udivdi3.o
> diff --git a/arch/riscv/lib/udivdi3.S b/arch/riscv/lib/udivdi3.S
> deleted file mode 100644
> index 3f07476a91a9..000000000000
> --- a/arch/riscv/lib/udivdi3.S
> +++ /dev/null
> @@ -1,32 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0-only */
> -/*
> - * Copyright (C) 2016-2017 Free Software Foundation, Inc.
> - */
> -
> -#include <linux/linkage.h>
> -
> -ENTRY(__udivdi3)
> -	mv	a2, a1
> -	mv	a1, a0
> -	li	a0, -1
> -	beqz	a2, .L5
> -	li	a3, 1
> -	bgeu	a2, a1, .L2
> -.L1:
> -	blez	a2, .L2
> -	slli	a2, a2, 1
> -	slli	a3, a3, 1
> -	bgtu	a1, a2, .L1
> -.L2:
> -	li	a0, 0
> -.L3:
> -	bltu	a1, a2, .L4
> -	sub	a1, a1, a2
> -	or	a0, a0, a3
> -.L4:
> -	srli	a3, a3, 1
> -	srli	a2, a2, 1
> -	bnez	a3, .L3
> -.L5:
> -	ret
> -ENDPROC(__udivdi3)
> -- 
> 2.21.0
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
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Re: [PATCH] RISC-V: Remove udivdi3

[Paul Walmsley]

On Wed, 7 Aug 2019, Alan Kao wrote:

> On Tue, Aug 06, 2019 at 05:05:08PM -0700, Palmer Dabbelt wrote:
> > This should never have landed in the first place: it was added as part
> > of 64-bit divide support for 32-bit systems, but the kernel doesn't
> > allow this sort of division.  I must have forgotten to remove it.
> > 
> > This patch removes the support.  Since this routine only worked on
> > 64-bit platforms but was only built on 32-bit platforms, it's
> > essentially just nonsense anyway.
> > 
> 
> It would be more complete if we add
> "Reported-by: Eric Lin <tesheng@andestech.com>" here.
> 
> > Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
> > Acked-by: Nicolas Pitre <nico@fluxnic.net>

Thanks, queued for v5.3-rc with Eric's Reported-by.


- Paul

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Re: [PATCH] RISC-V: Remove udivdi3

[Paul Walmsley]

On Tue, 6 Aug 2019, Paul Walmsley wrote:

> On Wed, 7 Aug 2019, Alan Kao wrote:
> 
> > On Tue, Aug 06, 2019 at 05:05:08PM -0700, Palmer Dabbelt wrote:
> > > This should never have landed in the first place: it was added as part
> > > of 64-bit divide support for 32-bit systems, but the kernel doesn't
> > > allow this sort of division.  I must have forgotten to remove it.
> > > 
> > > This patch removes the support.  Since this routine only worked on
> > > 64-bit platforms but was only built on 32-bit platforms, it's
> > > essentially just nonsense anyway.
> > > 
> > 
> > It would be more complete if we add
> > "Reported-by: Eric Lin <tesheng@andestech.com>" here.
> > 
> > > Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
> > > Acked-by: Nicolas Pitre <nico@fluxnic.net>
> 
> Thanks, queued for v5.3-rc with Eric's Reported-by.

This patch breaks the rv32_defconfig build, since udelay() still relies on 
__udivdi3().  I'll queue "riscv: delay: use do_div() instead of 
__udivdi3()" along with it: 

https://lore.kernel.org/linux-riscv/alpine.DEB.2.21.9999.1908061906240.25231@viisi.sifive.com/T/#u


- Paul

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Re: [PATCH] RISC-V: Remove udivdi3

[Nicolas Pitre]

On Tue, 6 Aug 2019, Paul Walmsley wrote:

> This patch breaks the rv32_defconfig build, since udelay() still relies on 
> __udivdi3().  I'll queue "riscv: delay: use do_div() instead of 
> __udivdi3()" along with it: 
> 
> https://lore.kernel.org/linux-riscv/alpine.DEB.2.21.9999.1908061906240.25231@viisi.sifive.com/T/#u

> +       u64 n;
> +       u32 rem;
> 
>         if (unlikely(usecs > MAX_UDELAY_US)) {
> -               __delay((u64)usecs * riscv_timebase / 1000000ULL);
> +               n = (u64)usecs * riscv_timebase;
> +               rem = do_div(n, 1000000);

You may omit rem and ignore the return value here.


Nicolas

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Re: [PATCH] RISC-V: Remove udivdi3

[Paul Walmsley]

On Tue, 6 Aug 2019, Nicolas Pitre wrote:

> On Tue, 6 Aug 2019, Paul Walmsley wrote:
> 
> > This patch breaks the rv32_defconfig build, since udelay() still relies on 
> > __udivdi3().  I'll queue "riscv: delay: use do_div() instead of 
> > __udivdi3()" along with it: 
> > 
> > https://lore.kernel.org/linux-riscv/alpine.DEB.2.21.9999.1908061906240.25231@viisi.sifive.com/T/#u
> 
> > +       u64 n;
> > +       u32 rem;
> > 
> >         if (unlikely(usecs > MAX_UDELAY_US)) {
> > -               __delay((u64)usecs * riscv_timebase / 1000000ULL);
> > +               n = (u64)usecs * riscv_timebase;
> > +               rem = do_div(n, 1000000);
> 
> You may omit rem and ignore the return value here.

Thanks Nico.  Updated patch below


- Paul

From: Paul Walmsley <paul.walmsley@sifive.com>
Date: Tue, 6 Aug 2019 18:28:33 -0700
Subject: [PATCH] riscv: delay: use do_div() instead of __udivdi3()

In preparation for removing __udivdi3() from the RISC-V
architecture-specific files, convert its one user to use do_div().
This avoids breaking the RV32 build after __udivdi3() is removed.

This second version removes the assignment of the remainder to an
unused temporary variable.  Thanks to Nicolas Pitre <nico@fluxnic.net>
for the suggestion.

Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Nicolas Pitre <nico@fluxnic.net>
---
 arch/riscv/lib/delay.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/lib/delay.c b/arch/riscv/lib/delay.c
index 87ff89e88f2c..f51c9a03bca1 100644
--- a/arch/riscv/lib/delay.c
+++ b/arch/riscv/lib/delay.c
@@ -81,9 +81,13 @@ EXPORT_SYMBOL(__delay);
 void udelay(unsigned long usecs)
 {
 	u64 ucycles = (u64)usecs * lpj_fine * UDELAY_MULT;
+	u64 n;
 
 	if (unlikely(usecs > MAX_UDELAY_US)) {
-		__delay((u64)usecs * riscv_timebase / 1000000ULL);
+		n = (u64)usecs * riscv_timebase;
+		do_div(n, 1000000);
+
+		__delay(n);
 		return;
 	}
 
-- 
2.22.0


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