Re: [PATCH v2 02/10] irqchip: add irqchip driver for nuc900

[Jason Cooper]

Wan ZongShun,

On Fri, Jul 15, 2016 at 12:02:55PM +0200, Arnd Bergmann wrote:
> On Friday, July 15, 2016 5:44:50 PM CEST Wan ZongShun wrote:
> > 2016-07-15 15:00 GMT+08:00 Arnd Bergmann <arnd@xxxxxxxx>:
> > > On Friday, July 15, 2016 1:15:58 PM CEST Wan Zongshun wrote:
...
> > > That assumes that REG_AIC_IPER contains a 32-bit value with one single
> > > bit set to indicate which IRQ was triggered.
> > >
> > > If the difference is only in performance, you could try measuring which
> > > of the two ends up being faster.
> > 
> > It seems hard to measure. I think Do IO operation should be slower
> > than shift 2. 
> 
> It depends on how fast that particular I/O path is. A lot of readl()
> operations are awfully slow, but the hardware design for the interrupt
> controller may in fact have optimized this to be reasonably fast.
> 
> Another option would be to avoid the shift and just use the raw value
> of the REG_AIC_IPER register as the hwirq, with a custom map()
> callback that turns shifts the number read from the DT two bits
> so it matches the register value.

Good idea.  Are the two lsb bits constant or do they need to be masked?

thx,

Jason.