Re: [RFC] fbdev/riva:change to use generice function to implement reverse_order()

yalin wang
2015-08-20T11:31:10Z

> On Aug 20, 2015, at 19:02, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
>
>
> On 10/08/15 13:12, yalin wang wrote:
>> This change to use swab32(bitrev32()) to implement reverse_order()
>> function, have better performance on some platforms.
>
> Which platforms? Presuming you tested this, roughly how much better
> performance? If you didn't, how do you know it's faster?

i investigate on arm64 platforms:

for (j = dsize; j--;) {
tmp = data[k++];
tmp = reverse_order(tmp);
NVDmaNext(par, tmp);
bac: 110006a4 add w4, w21, #0x1
bb0: 5ac000a3 rbit w3, w5

if (dsize) {
NVDmaStart(info, par, RECT_EXPAND_TWO_COLOR_DATA(0), dsize);

for (j = dsize; j--;) {
tmp = data[k++];
bb4: 110006d6 add w22, w22, #0x1
bb8: 5ac00861 rev w1, w3
tmp = reverse_order(tmp);
NVDmaNext(par, tmp);
bbc: b9041e64 str w4, [x19,#1052]
bc0: 8b3548c2 add x2, x6, w21, uxtw #2
bc4: b9000041 str w1, [x2]

this is the disassemble code after apply the patch,
only need:
rbit w3, w5
rev w1, w3
2 instruction to get the reverse_order() result,
apparently after than the origianl macro code.

>
>> Signed-off-by: yalin wang <yalin.wang2010@gmail.com>
>> ---
>> drivers/video/fbdev/riva/fbdev.c | 19 ++++++-------------
>> 1 file changed, 6 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/video/fbdev/riva/fbdev.c b/drivers/video/fbdev/riva/fbdev.c
>> index f1ad274..4803901 100644
>> --- a/drivers/video/fbdev/riva/fbdev.c
>> +++ b/drivers/video/fbdev/riva/fbdev.c
>> @@ -40,6 +40,7 @@
>> #include <linux/init.h>
>> #include <linux/pci.h>
>> #include <linux/backlight.h>
>> +#include <linux/swab.h>
>> #include <linux/bitrev.h>
>> #ifdef CONFIG_PMAC_BACKLIGHT
>> #include <asm/machdep.h>
>> @@ -84,6 +85,7 @@
>> #define SetBit(n) (1<<(n))
>> #define Set8Bits(value) ((value)&0xff)
>>
>> +#define reverse_order(v) swab32(bitrev32(v))
>> /* HW cursor parameters */
>> #define MAX_CURS 32
>>
>> @@ -451,15 +453,6 @@ static inline unsigned char MISCin(struct riva_par *par)
>> return (VGA_RD08(par->riva.PVIO, 0x3cc));
>> }
>>
>> -static inline void reverse_order(u32 *l)
>
> I would suggest to do the work in the inline function, instead of a
> macro. And if you keep the function prototype the same, then the changes
> to each reverse_order call site are not needed.
>

ok, i will change to a inline function.