[PATCH 3/3] mach64: optimize wait_for_fifo

[Bartlomiej Zolnierkiewicz]

On 08/27/2018 02:55 PM, Ville Syrjälä wrote:
> On Sat, Aug 25, 2018 at 03:54:17PM -0400, Mikulas Patocka wrote:
>> This is a simple optimization for fifo waiting that improves scrolling
>> performance by 5%. If the queue has more free entries that what we
>> consume, we can skip the costly register read next time.
>>
>> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
>>
>> ---
>>  drivers/video/fbdev/aty/atyfb.h        |   12 ++++++++----
>>  drivers/video/fbdev/aty/mach64_accel.c |    4 +++-
>>  2 files changed, 11 insertions(+), 5 deletions(-)
>>
>> Index: linux-stable/drivers/video/fbdev/aty/atyfb.h
>> ===================================================================
>> --- linux-stable.orig/drivers/video/fbdev/aty/atyfb.h	2018-08-25 21:49:16.000000000 +0200
>> +++ linux-stable/drivers/video/fbdev/aty/atyfb.h	2018-08-25 21:52:51.000000000 +0200
>> @@ -147,6 +147,7 @@ struct atyfb_par {
>>  	u16 pci_id;
>>  	u32 accel_flags;
>>  	int blitter_may_be_busy;
>> +	unsigned fifo_space;
>>  	int asleep;
>>  	int lock_blank;
>>  	unsigned long res_start;
>> @@ -346,10 +347,13 @@ extern int aty_init_cursor(struct fb_inf
>>       *  Hardware acceleration
>>       */
>>  
>> -static inline void wait_for_fifo(u16 entries, const struct atyfb_par *par)
>> +static inline void wait_for_fifo(u16 entries, struct atyfb_par *par)
>>  {
>> -	while ((aty_ld_le32(FIFO_STAT, par) & 0xffff) >
>> -	       ((u32) (0x8000 >> entries)));
>> +	unsigned fifo_space = par->fifo_space;
>> +	while (entries > fifo_space) {
>> +		fifo_space = 16 - fls(aty_ld_le32(FIFO_STAT, par) & 0xffff);
> 
> I don't recall off hand which way this register works, but based
> on the existing code this looks correct.
> 
> Reviewed-by: Ville Syrjälä <syrjala at sci.fi>

Patch queued for 4.20, thanks.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics