Re: [PATCH] irqchip/versatile-fpga: Handle chained IRQs properly

Hi Marc,

On 2020-03-19 02:48, Marc Zyngier wrote:
> Hi Sungbo,
> 
> On 2020-03-18 17:09, Sungbo Eo wrote:
>> Enclose the chained handler with chained_irq_{enter,exit}(), so that the
>> muxed interrupts get properly acked.
>>
>> This patch also fixes a reboot bug on OX820 SoC, where the jiffies timer
>> interrupt is never acked. The kernel waits a clock tick forever in
>> calibrate_delay_converge(), which leads to a boot hang.
> 
> Nice catch.
> 
>>
>> Signed-off-by: Sungbo Eo <[email protected]>
>> Cc: Neil Armstrong <[email protected]>
>> ---
>>  drivers/irqchip/irq-versatile-fpga.c | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/irqchip/irq-versatile-fpga.c
>> b/drivers/irqchip/irq-versatile-fpga.c
>> index 928858dada75..08faab2fec3e 100644
>> --- a/drivers/irqchip/irq-versatile-fpga.c
>> +++ b/drivers/irqchip/irq-versatile-fpga.c
>> @@ -6,6 +6,7 @@
>>  #include <linux/irq.h>
>>  #include <linux/io.h>
>>  #include <linux/irqchip.h>
>> +#include <linux/irqchip/chained_irq.h>
>>  #include <linux/irqchip/versatile-fpga.h>
>>  #include <linux/irqdomain.h>
>>  #include <linux/module.h>
>> @@ -68,12 +69,15 @@ static void fpga_irq_unmask(struct irq_data *d)
>>
>>  static void fpga_irq_handle(struct irq_desc *desc)
>>  {
>> +    struct irq_chip *chip = irq_desc_get_chip(desc);
>>      struct fpga_irq_data *f = irq_desc_get_handler_data(desc);
>>      u32 status = readl(f->base + IRQ_STATUS);
>>
>> +    chained_irq_enter(chip, desc);
>> +
> 
> It's probably not a big deal, but I'm not fond of starting talking to
> the muxing irqchip before having done the chained_irq_enter() call.
> 
> Moving that read here would probably be safer.

Oops, I missed it. Thanks for pointing it out.

> 
>>      if (status == 0) {
>>          do_bad_IRQ(desc);
>> -        return;
>> +        goto out;
>>      }
>>
>>      do {
>> @@ -82,6 +86,9 @@ static void fpga_irq_handle(struct irq_desc *desc)
>>          status &= ~(1 << irq);
>>          generic_handle_irq(irq_find_mapping(f->domain, irq));
>>      } while (status);
>> +
>> +out:
>> +    chained_irq_exit(chip, desc);
>>  }
>>
>>  /*
> 
> Otherwise looks good. If you send it again with the above fixed
> and a Fixes: tag, I'll queue it.

It seems the handler had been broken from the very beginning. Could you 
give me a hint on how the tag should be like?

Thanks.

> 
> Thanks,
> 
>          M.