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SubjectRe: [PATCH] irqchip: mips-cpu: Remove eoi operation
On 2020-01-14 23:30, Paul Burton wrote:
> Hi Jiaxun,
>
> On Mon, Jan 13, 2020 at 06:12:51PM +0800, Jiaxun Yang wrote:
>> The eoi opreation in mips_cpu_irq_controller caused chained_irq_enter
>> falsely consider CPU IP interrupt as a FastEOI type IRQ. So the
>> interrupt
>> won't be masked during in handler. Which might lead to spurious
>> interrupt.
>>
>> Thus we simply remove eoi operation for mips_cpu_irq_controller,
>>
>> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
>> ---
>> drivers/irqchip/irq-mips-cpu.c | 1 -
>> 1 file changed, 1 deletion(-)
>>
>> diff --git a/drivers/irqchip/irq-mips-cpu.c
>> b/drivers/irqchip/irq-mips-cpu.c
>> index 95d4fd8f7a96..0ad7f1f9a58b 100644
>> --- a/drivers/irqchip/irq-mips-cpu.c
>> +++ b/drivers/irqchip/irq-mips-cpu.c
>> @@ -55,7 +55,6 @@ static struct irq_chip mips_cpu_irq_controller = {
>> .irq_mask = mask_mips_irq,
>> .irq_mask_ack = mask_mips_irq,
>> .irq_unmask = unmask_mips_irq,
>> - .irq_eoi = unmask_mips_irq,
>> .irq_disable = mask_mips_irq,
>> .irq_enable = unmask_mips_irq,
>> };
>
> This one scares me; something doesn't seem right. The irq_eoi (née eoi)
> callback was first added way back in commit 1417836e81c0 ("[MIPS] use
> generic_handle_irq, handle_level_irq, handle_percpu_irq"). The commit
> message there states that the motivation was to allow use of
> handle_percpu_irq(), and indeed handle_percpu_irq() does:
>
> irq_ack() (ie. mask)
> invoke the handler(s)
> irq_eoi() (ie. unmask)
>
> By removing the irq_eoi callback I don't see how we'd ever unmask the
> interrupt again..?

To be completely blunt, the fact that unmask and eoi are implemented the
same way is a clear sign that this is a bit broken.

irq_eoi is used if the irqchip tracks the IRQ life-cycle in HW, and it's
not obvious that this is the case. The fact that ack is also mapped to
mask
just adds to my feeling...

M.
--
Jazz is not dead. It just smells funny...

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