* [PATCH] powerpc/8xx: Fix do_mtspr_cpu6 build on older compilers
@ 2016-03-15 6:25 Scott Wood
2016-03-15 10:18 ` Christophe Leroy
0 siblings, 1 reply; 3+ messages in thread
From: Scott Wood @ 2016-03-15 6:25 UTC (permalink / raw)
To: Michael Ellerman; +Cc: linuxppc-dev, Scott Wood, Christophe Leroy
Some versions of GCC, reportedly before 4.9, fail with
arch/powerpc/mm/8xx_mmu.c:139:2: error: memory input 1 is not directly
addressable
Use a register constraint instead of a memory constraint to avoid this.
Also change the one-element array into a simple variable.
Signed-off-by: Scott Wood <oss@buserror.net>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
---
Christope, could you test? And was there any particular reason for the [1]?
arch/powerpc/include/asm/reg_8xx.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/include/asm/reg_8xx.h b/arch/powerpc/include/asm/reg_8xx.h
index d41412c..cb7dfb9 100644
--- a/arch/powerpc/include/asm/reg_8xx.h
+++ b/arch/powerpc/include/asm/reg_8xx.h
@@ -53,11 +53,11 @@
#ifdef CONFIG_8xx_CPU6
#define do_mtspr_cpu6(rn, rn_addr, v) \
do { \
- int _reg_cpu6 = rn_addr, _tmp_cpu6[1]; \
- asm volatile("stw %0, %1;" \
- "lwz %0, %1;" \
+ int _reg_cpu6 = rn_addr, _tmp_cpu6; \
+ asm volatile("stwx %0, 0, %1;" \
+ "lwzx %0, 0, %1;" \
"mtspr " __stringify(rn) ",%2" : \
- : "r" (_reg_cpu6), "m"(_tmp_cpu6), \
+ : "r" (_reg_cpu6), "r" (&_tmp_cpu6), \
"r" ((unsigned long)(v)) \
: "memory"); \
} while (0)
--
2.5.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] powerpc/8xx: Fix do_mtspr_cpu6 build on older compilers
2016-03-15 6:25 [PATCH] powerpc/8xx: Fix do_mtspr_cpu6 build on older compilers Scott Wood
@ 2016-03-15 10:18 ` Christophe Leroy
2016-03-15 17:35 ` Scott Wood
0 siblings, 1 reply; 3+ messages in thread
From: Christophe Leroy @ 2016-03-15 10:18 UTC (permalink / raw)
To: Scott Wood, Michael Ellerman; +Cc: linuxppc-dev
Le 15/03/2016 07:25, Scott Wood a écrit :
> Some versions of GCC, reportedly before 4.9, fail with
> arch/powerpc/mm/8xx_mmu.c:139:2: error: memory input 1 is not directly
> addressable
>
> Use a register constraint instead of a memory constraint to avoid this.
> Also change the one-element array into a simple variable.
>
> Signed-off-by: Scott Wood <oss@buserror.net>
> Cc: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
> Christope, could you test? And was there any particular reason for the [1]?
As far as I remember the idea behind the [1] was to ensure that the
variable was allocated from stack memory and not optimised in a register.
I will not be able to test it as I don't have any CPU suffering CPU6
errata, but I observe that the result of your patch doesn't exactly
match the solution proposed by Freescale in the ERRATA:
MPC860 CPU6 ERRATA says:
each "mtspr" instruction which accesses one of these registers must be
preceded by a store word and a
load word instruction of a data operand equal to the spr_address of the
respective register. As an
example, to write the data from the general purpose register r1 to the
special purpose register
M_TW, the procedure in Table 6 should be followed:
Table 6. Writing Data from r1 to M_TW:
lis r2, some address_msb
li r3, 0x3f80
stw r3, some address_lsb(r2)
lwz r3, some address_lsb(r2)
mtspr M_TW, r1
Without your patch (with gcc 4.8.3), I get:
c000d8cc <set_context>:
[...]
c000d8f4: 39 40 3f 80 li r10,16256
c000d8f8: 91 41 00 08 stw r10,8(r1)
c000d8fc: 81 41 00 08 lwz r10,8(r1)
c000d900: 7d 3f c3 a6 mtspr 799,r9
c000d904: 39 20 33 80 li r9,13184
c000d908: 91 21 00 08 stw r9,8(r1)
c000d90c: 81 21 00 08 lwz r9,8(r1)
c000d910: 7c 79 c3 a6 mtspr 793,r3
[...]
With your patch (with gcc 4.8.3), I get:
c000d8dc <set_context>:
[...]
c000d904: 39 40 3f 80 li r10,16256
c000d908: 39 21 00 08 addi r9,r1,8
c000d90c: 7d 40 49 2e stwx r10,0,r9
c000d910: 7d 40 48 2e lwzx r10,0,r9
c000d914: 7d 1f c3 a6 mtspr 799,r8
c000d918: 39 40 33 80 li r10,13184
c000d91c: 7d 40 49 2e stwx r10,0,r9
c000d920: 7d 40 48 2e lwzx r10,0,r9
c000d924: 7c 79 c3 a6 mtspr 793,r3
[...]
I'm not able to tell if using stwx/lwzx instead of stw/lwz is valid.
Christophe
>
> arch/powerpc/include/asm/reg_8xx.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/reg_8xx.h b/arch/powerpc/include/asm/reg_8xx.h
> index d41412c..cb7dfb9 100644
> --- a/arch/powerpc/include/asm/reg_8xx.h
> +++ b/arch/powerpc/include/asm/reg_8xx.h
> @@ -53,11 +53,11 @@
> #ifdef CONFIG_8xx_CPU6
> #define do_mtspr_cpu6(rn, rn_addr, v) \
> do { \
> - int _reg_cpu6 = rn_addr, _tmp_cpu6[1]; \
> - asm volatile("stw %0, %1;" \
> - "lwz %0, %1;" \
> + int _reg_cpu6 = rn_addr, _tmp_cpu6; \
> + asm volatile("stwx %0, 0, %1;" \
> + "lwzx %0, 0, %1;" \
> "mtspr " __stringify(rn) ",%2" : \
> - : "r" (_reg_cpu6), "m"(_tmp_cpu6), \
> + : "r" (_reg_cpu6), "r" (&_tmp_cpu6), \
> "r" ((unsigned long)(v)) \
> : "memory"); \
> } while (0)
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] powerpc/8xx: Fix do_mtspr_cpu6 build on older compilers
2016-03-15 10:18 ` Christophe Leroy
@ 2016-03-15 17:35 ` Scott Wood
0 siblings, 0 replies; 3+ messages in thread
From: Scott Wood @ 2016-03-15 17:35 UTC (permalink / raw)
To: Christophe Leroy, Michael Ellerman; +Cc: linuxppc-dev
On Tue, 2016-03-15 at 11:18 +0100, Christophe Leroy wrote:
> Le 15/03/2016 07:25, Scott Wood a écrit :
> > Some versions of GCC, reportedly before 4.9, fail with
> > arch/powerpc/mm/8xx_mmu.c:139:2: error: memory input 1 is not directly
> > addressable
> >
> > Use a register constraint instead of a memory constraint to avoid this.
> > Also change the one-element array into a simple variable.
> >
> > Signed-off-by: Scott Wood <oss@buserror.net>
> > Cc: Christophe Leroy <christophe.leroy@c-s.fr>
> > ---
> > Christope, could you test? And was there any particular reason for the
> > [1]?
> As far as I remember the idea behind the [1] was to ensure that the
> variable was allocated from stack memory and not optimised in a register.
Taking the address of it should accomplish that.
> I will not be able to test it as I don't have any CPU suffering CPU6
> errata,
I'm wondering if anyone using current kernels cares about chips that have this
erratum. Maybe it's time to remove support for them.
> but I observe that the result of your patch doesn't exactly
> match the solution proposed by Freescale in the ERRATA:
>
> MPC860 CPU6 ERRATA says:
> each "mtspr" instruction which accesses one of these registers must be
> preceded by a store word and a
> load word instruction of a data operand equal to the spr_address of the
> respective register. As an
> example, to write the data from the general purpose register r1 to the
> special purpose register
> M_TW, the procedure in Table 6 should be followed:
>
> Table 6. Writing Data from r1 to M_TW:
> lis r2, some address_msb
> li r3, 0x3f80
> stw r3, some address_lsb(r2)
> lwz r3, some address_lsb(r2)
> mtspr M_TW, r1
>
> Without your patch (with gcc 4.8.3), I get:
> c000d8cc <set_context>:
> [...]
> c000d8f4: 39 40 3f 80 li r10,16256
> c000d8f8: 91 41 00 08 stw r10,8(r1)
> c000d8fc: 81 41 00 08 lwz r10,8(r1)
> c000d900: 7d 3f c3 a6 mtspr 799,r9
> c000d904: 39 20 33 80 li r9,13184
> c000d908: 91 21 00 08 stw r9,8(r1)
> c000d90c: 81 21 00 08 lwz r9,8(r1)
> c000d910: 7c 79 c3 a6 mtspr 793,r3
> [...]
>
> With your patch (with gcc 4.8.3), I get:
> c000d8dc <set_context>:
> [...]
> c000d904: 39 40 3f 80 li r10,16256
> c000d908: 39 21 00 08 addi r9,r1,8
> c000d90c: 7d 40 49 2e stwx r10,0,r9
> c000d910: 7d 40 48 2e lwzx r10,0,r9
> c000d914: 7d 1f c3 a6 mtspr 799,r8
> c000d918: 39 40 33 80 li r10,13184
> c000d91c: 7d 40 49 2e stwx r10,0,r9
> c000d920: 7d 40 48 2e lwzx r10,0,r9
> c000d924: 7c 79 c3 a6 mtspr 793,r3
> [...]
>
> I'm not able to tell if using stwx/lwzx instead of stw/lwz is valid.
It says "a store word and a load word instruction". lwzx is a load word
instruction just as lwz is.
-Scott
^ permalink raw reply [flat|nested] 3+ messages in thread
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2016-03-15 6:25 [PATCH] powerpc/8xx: Fix do_mtspr_cpu6 build on older compilers Scott Wood
2016-03-15 10:18 ` Christophe Leroy
2016-03-15 17:35 ` Scott Wood
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