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?
Sebastian
>> Signed-off-by: Sebastian Hesselbarth <sebastian.hesselba...@gmail.com>
>> Acked-by: Jason Cooper <ja...@lakedaemon.net>
>> ---
>> Cc: Jason Cooper <ja...@lakedaemon.net>
>> Cc: Andrew Lunn <and...@lunn.ch>
>> Cc: Gregory Clement <gregory.clem...@free-electrons.com>
>> Cc: Thomas Gleixner <t...@linutronix.de>
>> Cc: linux-arm-ker...@lists.infradead.org
>> Cc: linux-kernel@vger.kernel.org
>> ---
>> drivers/irqchip/irq-orion.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-orion.c b/drivers/irqchip/irq-orion.c
>> index e25f246cd2fb..34d18b48bb78 100644
>> --- a/drivers/irqchip/irq-orion.c
>> +++ b/drivers/irqchip/irq-orion.c
>> @@ -42,7 +42,7 @@ __exception_irq_entry orion_handle_irq(struct pt_regs
>> *regs)
>> u32 stat = readl_relaxed(gc->reg_base + ORION_IRQ_CAUSE) &
>> gc->mask_cache;
>> while (stat) {
>> - u32 hwirq = ffs(stat) - 1;
>> + u32 hwirq = __fls(stat);
>> u32 irq = irq_find_mapping(orion_irq_domain,
>> gc->irq_base + hwirq);
>> handle_IRQ(irq, regs);
>> @@ -117,7 +117,7 @@ static void orion_bridge_irq_handler(unsigned int irq,
>> struct irq_desc *desc)
>> gc->mask_cache;
>>
>> while (stat) {
>> - u32 hwirq = ffs(stat) - 1;
>> + u32 hwirq = __fls(stat);
>>
>> generic_handle_irq(irq_find_mapping(d, gc->irq_base + hwirq));
>> stat &= ~(1 << hwirq);
>> --
>> 1.9.1
>>
>>
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