[PATCH 62/62] ARM: tegra: make debug_ll code build for ARMv6

[PATCH 62/62] ARM: tegra: make debug_ll code build for ARMv6

[Arnd Bergmann]

In a combined ARMv6/v7 kernel, we cannot use the
movt/movw instructions to load an immediate, as they
are not valid on ARMv6.

This changes the file to use an indirect load instead,
as lots of other implementations do.

Signed-off-by: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
Cc: Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>
Cc: Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
---
 arch/arm/include/debug/tegra.S | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/arch/arm/include/debug/tegra.S b/arch/arm/include/debug/tegra.S
index f98763f..3bc8059 100644
--- a/arch/arm/include/debug/tegra.S
+++ b/arch/arm/include/debug/tegra.S
@@ -53,8 +53,7 @@
 
 #define checkuart(rp, rv, lhu, bit, uart) \
 		/* Load address of CLK_RST register */ \
-		movw	rp, #TEGRA_CLK_RST_DEVICES_##lhu & 0xffff ; \
-		movt	rp, #TEGRA_CLK_RST_DEVICES_##lhu >> 16 ; \
+		ldr	rp, =TEGRA_CLK_RST_DEVICES_##lhu ; \
 		/* Load value from CLK_RST register */ \
 		ldr	rp, [rp, #0] ; \
 		/* Test UART's reset bit */ \
@@ -62,8 +61,7 @@
 		/* If set, can't use UART; jump to save no UART */ \
 		bne	90f ; \
 		/* Load address of CLK_OUT_ENB register */ \
-		movw	rp, #TEGRA_CLK_OUT_ENB_##lhu & 0xffff ; \
-		movt	rp, #TEGRA_CLK_OUT_ENB_##lhu >> 16 ; \
+		ldr	rp, =TEGRA_CLK_OUT_ENB_##lhu ; \
 		/* Load value from CLK_OUT_ENB register */ \
 		ldr	rp, [rp, #0] ; \
 		/* Test UART's clock enable bit */ \
@@ -71,8 +69,7 @@
 		/* If clear, can't use UART; jump to save no UART */ \
 		beq	90f ; \
 		/* Passed all tests, load address of UART registers */ \
-		movw	rp, #TEGRA_UART##uart##_BASE & 0xffff ; \
-		movt	rp, #TEGRA_UART##uart##_BASE >> 16 ; \
+		ldr	rp, =TEGRA_UART##uart##_BASE ; \
 		/* Jump to save UART address */ \
 		b 91f
 
@@ -90,15 +87,16 @@
 
 #ifdef CONFIG_TEGRA_DEBUG_UART_AUTO_ODMDATA
 		/* Check ODMDATA */
-10:		movw	\rp, #TEGRA_PMC_SCRATCH20 & 0xffff
-		movt	\rp, #TEGRA_PMC_SCRATCH20 >> 16
+10:		ldr	\rp, =TEGRA_PMC_SCRATCH20
 		ldr	\rp, [\rp, #0]		@ Load PMC_SCRATCH20
-		ubfx	\rv, \rp, #18, #2	@ 19:18 are console type
+		lsr	\rv, \rp, #18		@ 19:18 are console type
+		and	\rv, \rv, #3
 		cmp	\rv, #2			@ 2 and 3 mean DCC, UART
 		beq	11f			@ some boards swap the meaning
 		cmp	\rv, #3			@ so accept either
 		bne	90f
-11:		ubfx	\rv, \rp, #15, #3	@ 17:15 are UART ID
+11:		lsr	\rv, \rp, #15		@ 17:15 are UART ID
+		and	\rv, #7	
 		cmp	\rv, #0			@ UART 0?
 		beq	20f
 		cmp	\rv, #1			@ UART 1?
-- 
1.8.3.2

Re: [PATCH 62/62] ARM: tegra: make debug_ll code build for ARMv6

[Stephen Warren]

On 03/19/2014 01:29 PM, Arnd Bergmann wrote:
> In a combined ARMv6/v7 kernel, we cannot use the
> movt/movw instructions to load an immediate, as they
> are not valid on ARMv6.
> 
> This changes the file to use an indirect load instead,
> as lots of other implementations do.

Hmmm. This code is guaranteed to only execute on Tegra (well, perhaps
someone can turn on the wrong debug option and run it on non-Tegra, but
then it's guaranteed not to work since the HW it touches doesn't exist).
As such, the code ought to be able to use ARMv7 instructions.

As a fix for similar issues in assembly code in arch/arm/mach-tegra/*.S,
Makefile there does:

asflags-y                               += -march=armv7-a

(I think you added that? Yes, in 408e713545ca "ARM: tegra: build
assembly files with -march=armv7-a")

Shouldn't we use the same fix in this case too?

Re: [PATCH 62/62] ARM: tegra: make debug_ll code build for ARMv6

[Arnd Bergmann]

On Wednesday 19 March 2014 13:40:06 Stephen Warren wrote:
> Hmmm. This code is guaranteed to only execute on Tegra (well, perhaps
> someone can turn on the wrong debug option and run it on non-Tegra, but
> then it's guaranteed not to work since the HW it touches doesn't exist).
> As such, the code ought to be able to use ARMv7 instructions.
> 
> As a fix for similar issues in assembly code in arch/arm/mach-tegra/*.S,
> Makefile there does:
> 
> asflags-y                               += -march=armv7-a
> 
> (I think you added that? Yes, in 408e713545ca "ARM: tegra: build
> assembly files with -march=armv7-a")
> 
> Shouldn't we use the same fix in this case too?

That was my first idea, but I couldn't come up with a nice way to do this
for arch/arm/kernel/debug.S, which #includes the specific implementation.

I'd rather not put lots of per-platform hacks into arch/arm/kernel/Makefile.

	Arnd

Re: [PATCH 62/62] ARM: tegra: make debug_ll code build for ARMv6

[Stephen Warren]

On 03/19/2014 01:51 PM, Arnd Bergmann wrote:
> On Wednesday 19 March 2014 13:40:06 Stephen Warren wrote:
>> Hmmm. This code is guaranteed to only execute on Tegra (well, perhaps
>> someone can turn on the wrong debug option and run it on non-Tegra, but
>> then it's guaranteed not to work since the HW it touches doesn't exist).
>> As such, the code ought to be able to use ARMv7 instructions.
>>
>> As a fix for similar issues in assembly code in arch/arm/mach-tegra/*.S,
>> Makefile there does:
>>
>> asflags-y                               += -march=armv7-a
>>
>> (I think you added that? Yes, in 408e713545ca "ARM: tegra: build
>> assembly files with -march=armv7-a")
>>
>> Shouldn't we use the same fix in this case too?
> 
> That was my first idea, but I couldn't come up with a nice way to do this
> for arch/arm/kernel/debug.S, which #includes the specific implementation.
> 
> I'd rather not put lots of per-platform hacks into arch/arm/kernel/Makefile.

Oh, I guess the fact it's include makes it a bit more painful.

You could deal with it in Kconfig reasonably easily by having each of
DEBUG_*_UART select a config option indicating how to compile code that
includes DEBUG_LL_INCLUDE, and then have the Makefiles set up asflags
based on those. Still, that would be a lot of work and this patch is
simpler.

Tested-by: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Acked-by: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>

Re: [PATCH 62/62] ARM: tegra: make debug_ll code build for ARMv6

[Arnd Bergmann]

On Wednesday 19 March 2014, Stephen Warren wrote:
> On 03/19/2014 01:51 PM, Arnd Bergmann wrote:
> > On Wednesday 19 March 2014 13:40:06 Stephen Warren wrote:
> >> Hmmm. This code is guaranteed to only execute on Tegra (well, perhaps
> >> someone can turn on the wrong debug option and run it on non-Tegra, but
> >> then it's guaranteed not to work since the HW it touches doesn't exist).
> >> As such, the code ought to be able to use ARMv7 instructions.
> >>
> >> As a fix for similar issues in assembly code in arch/arm/mach-tegra/*.S,
> >> Makefile there does:
> >>
> >> asflags-y                               += -march=armv7-a
> >>
> >> (I think you added that? Yes, in 408e713545ca "ARM: tegra: build
> >> assembly files with -march=armv7-a")
> >>
> >> Shouldn't we use the same fix in this case too?
> > 
> > That was my first idea, but I couldn't come up with a nice way to do this
> > for arch/arm/kernel/debug.S, which #includes the specific implementation.
> > 
> > I'd rather not put lots of per-platform hacks into arch/arm/kernel/Makefile.
> 
> Oh, I guess the fact it's include makes it a bit more painful.
> 
> You could deal with it in Kconfig reasonably easily by having each of
> DEBUG_*_UART select a config option indicating how to compile code that
> includes DEBUG_LL_INCLUDE, and then have the Makefiles set up asflags
> based on those. Still, that would be a lot of work and this patch is
> simpler.
> 
> Tested-by: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> Acked-by: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>

Ok, thanks for testing! I'm always cautious aobut my own assembly skills,
so I'm glad this worked.

	Arnd