On Mon, Apr 28, 2014 at 10:06:25PM +0200, Sebastian Hesselbarth wrote: > On 04/28/2014 09:39 PM, Thomas Gleixner wrote: > > On Sat, 26 Apr 2014, Sebastian Hesselbarth wrote: > > > >> Non-DT irq handlers were working through irq causes from most-significant > >> to least-significant bit, while DT irqchip driver does it the other way > >> round. This revealed some more HW issues on Kirkwood peripheral IP, where > >> spurious sdio irqs can happen although IP's irq enable registers are all > >> zero. Although, not directly related with the described issue, reverse > >> irq bit handling back to original order by replacing ffs() with fls(). > > > > So why are we reverting to the original order? > > > > The explanation above is just confusing. > > Actually, I first wanted to reply "The original order worked for > years, so get back to it." But then I thought about finding a better > answer and remembered some comment of Russell a while ago. >
> I disassembled the generated binary and the original order saves two > instructions for each bit count using clz. > > With this patch: > 60: e3a07001 mov r7, #1 > 64: e16f3f14 clz r3, r4 > 68: e263301f rsb r3, r3, #31 > 6c: e1c44317 bic r4, r4, r7, lsl r3 > 70: e5951004 ldr r1, [r5, #4] > > Without this patch: > 60: e3a06001 mov r6, #1 > 64: e2643000 rsb r3, r4, #0 > 68: e0033004 and r3, r3, r4 > 6c: e16f3f13 clz r3, r3 > 70: e263301f rsb r3, r3, #31 > 74: e1c44316 bic r4, r4, r6, lsl r3 > 78: e5971004 ldr r1, [r7, #4] > You want me to reword the commit message accordingly? Please do. I would even quote the above. thx, Jason. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/