On Tue, Apr 01, 2014 at 05:44:19PM -0500, Felipe Balbi wrote:
> current algorithm in allocate_free_irq() is O(n),
> by just keeping track of last allocated IRQ with a
> simple unsigned integer, we can find a free IRQ
> in O(1).
>
> Signed-off-by: Felipe Balbi <balbi@xxxxxx>
> ---
>
> compile-tested only as J6 DTS is currently missing crossbar
> altogether :-(
>
> There's a drawback with this patch which I'm not sure if we
> should care a lot because I couldn't entirely grasp when is
> domain->xlate() called and if we will map/unmap IRQs in runtime
> or will this *always* be done only during boot.
>
> If we're talking about runtime IRQ remapping, then this, clearly,
> won't work. But if this will be done only during boot up, then we
> avoid iterating over the irq_map array each time we try to translate
> a new IRQ prior to mapping it.
>
> Comments are highly welcome as I'll probably learn something new
> about the IRQ subsystem ;-)
>
> drivers/irqchip/irq-crossbar.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/irqchip/irq-crossbar.c b/drivers/irqchip/irq-crossbar.c
> index fc817d2..1c4da5a 100644
> --- a/drivers/irqchip/irq-crossbar.c
> +++ b/drivers/irqchip/irq-crossbar.c
> @@ -31,6 +31,7 @@ struct crossbar_device {
> void __iomem *crossbar_base;
> int *register_offsets;
> void (*write) (int, int);
> + unsigned int current_irq;
> };
>
> static struct crossbar_device *cb;
> @@ -52,16 +53,15 @@ static inline void crossbar_writeb(int irq_no, int cb_no)
>
> static inline int allocate_free_irq(int cb_no)
> {
> - int i;
> + int current_irq;
>
> - for (i = 0; i < cb->int_max; i++) {
> - if (cb->irq_map[i] == IRQ_FREE) {
> - cb->irq_map[i] = cb_no;
> - return i;
> - }
> - }
> + if (cb->current_irq == cb->int_max)
> + return -ENODEV;
> +
> + current_irq = cb->current_irq++;
> + cb->irq_map[current_irq++] = cb_no;
this increment is bogus, thought I had committed already, please ignore.
--
balbi
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