[U-Boot] [RFC PATCH] ARM: byteorder: add optimized swab16 and swab32

[U-Boot] [RFC PATCH] ARM: byteorder: add optimized swab16 and swab32

[Dirk Behme]

Use the specialized ARM instructions for swapping 16 and 32 bit values
instead of using the generic ones from include/linux/byteorder/swab.h.

The x86 version in arch/x86/include/asm/byteorder.h was taken as an
example for this.

E.g. for the mx6qsabrelite target this results in ~4k less code.

Signed-off-by: Dirk Behme <dirk.behme@gmail.com>
---

This patch is marked as RFC due to two questions:

1) These ARM instructions are available in ARMv6 and above. Do we have to limit
   this code somehow to >= ARMv6? I couldn't find any #define to do this in
   U-Boot (?)

2) I'm not sure about the rev16. The rev16 instruction swaps *both* half words,
   the lower _and_ the upper one: 

   REV16 Rd, Rm => Rd[15:8] := Rm[7:0], Rd[7:0] := Rm[15:8], Rd[31:24] := Rm[23:16], Rd[23:16] := Rm[31:24]

   I'm not sure if we want this? Most probably we only want to swap the lower
   half word with swap16()?

 arch/arm/include/asm/byteorder.h |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/arm/include/asm/byteorder.h b/arch/arm/include/asm/byteorder.h
index c3489f1..f21baf0 100644
--- a/arch/arm/include/asm/byteorder.h
+++ b/arch/arm/include/asm/byteorder.h
@@ -15,6 +15,23 @@
 #ifndef __ASM_ARM_BYTEORDER_H
 #define __ASM_ARM_BYTEORDER_H
 
+static __inline__ __u32 ___arch__swab32(__u32 x)
+{
+	__asm__("rev %0,%1"		/* swap bytes */ \
+		: "=r" (x) \
+		:  "0" (x)); \
+		return x;
+}
+#define __arch__swab32(x) ___arch__swab32(x)
+
+static __inline__ __u16 ___arch__swab16(__u16 x)
+{
+	__asm__("rev16 %0,%1"		/* swap bytes */ \
+		: "=r" (x) \
+		:  "0" (x)); \
+		return x;
+}
+#define __arch__swab16(x) ___arch__swab16(x)
 
 #include <asm/types.h>
 
-- 
1.7.10.4

[U-Boot] [RFC PATCH] ARM: byteorder: add optimized swab16 and swab32

[Måns Rullgård]

Dirk Behme <dirk.behme@gmail.com> writes:

> Use the specialized ARM instructions for swapping 16 and 32 bit values
> instead of using the generic ones from include/linux/byteorder/swab.h.
>
> The x86 version in arch/x86/include/asm/byteorder.h was taken as an
> example for this.
>
> E.g. for the mx6qsabrelite target this results in ~4k less code.

Which compiler are you using?  GCC 4.5 and later recognises the byteswap
pattern and emits these instructions automatically.  This gives better
code than the inline asm since it allows the compiler to do proper
instruction scheduling, and in the 16-bit case it avoids extraneous
masking.

-- 
M?ns Rullg?rd
mans at mansr.com

[U-Boot] [RFC PATCH] ARM: byteorder: add optimized swab16 and swab32

[Dirk Behme]

Am 10.05.2013 18:56, schrieb M?ns Rullg?rd:
> Dirk Behme <dirk.behme@gmail.com> writes:
>
>> Use the specialized ARM instructions for swapping 16 and 32 bit values
>> instead of using the generic ones from include/linux/byteorder/swab.h.
>>
>> The x86 version in arch/x86/include/asm/byteorder.h was taken as an
>> example for this.
>>
>> E.g. for the mx6qsabrelite target this results in ~4k less code.
>
> Which compiler are you using?

An older gcc 4.4.4 version.

> GCC 4.5 and later recognises the byteswap
> pattern and emits these instructions automatically.  This gives better
> code than the inline asm since it allows the compiler to do proper
> instruction scheduling, and in the 16-bit case it avoids extraneous
> masking.

Thanks,

Dirk

[U-Boot] [RFC PATCH] ARM: byteorder: add optimized swab16 and swab32

[Wolfgang Denk]

Dear Dirk Behme,

In message <518D3191.7060205@gmail.com> you wrote:
>
> > Which compiler are you using?
> 
> An older gcc 4.4.4 version.

We should not really care about these.  And if so, then onlya fter
testing we are really suing such old stuff, i. e. those who are using
recent tools (eventually the majority of users) should not suffer from
hacst to optimize for ancient code.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Only two things are infinite,  the universe and human stupidity,  and
I'm not sure about the former.                     -- Albert Einstein