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

[Marc Zyngier]

On 2020-03-18 18:20, Sungbo Eo wrote:
> 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 <mans0n@xxxxxxxxxx>
> > > Cc: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
> > > ---
> > > Âdrivers/irqchip/irq-versatile-fpga.c | 9 ++++++++-
> > > Â1 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 @@
> > > Â#include <linux/irq.h>
> > > Â#include <linux/io.h>
> > > Â#include <linux/irqchip.h>
> > > +#include <linux/irqchip/chained_irq.h>
> > > Â#include <linux/irqchip/versatile-fpga.h>
> > > Â#include <linux/irqdomain.h>
> > > Â#include <linux/module.h>
> > > @@ -68,12 +69,15 @@ static void fpga_irq_unmask(struct irq_data *d)
> > >
> > > Âstatic void fpga_irq_handle(struct irq_desc *desc)
> > > Â{
> > > +ÂÂÂ struct irq_chip *chip = irq_desc_get_chip(desc);
> > > ÂÂÂÂ struct fpga_irq_data *f = irq_desc_get_handler_data(desc);
> > > ÂÂÂÂ u32 status = readl(f->base + IRQ_STATUS);
> > >
> > > +ÂÂÂ 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.
>
> > > ÂÂÂÂ if (status == 0) {
> > > ÂÂÂÂÂÂÂÂ do_bad_IRQ(desc);
> > > -ÂÂÂÂÂÂÂ return;
> > > +ÂÂÂÂÂÂÂ goto out;
> > > ÂÂÂÂ }
> > >
> > > ÂÂÂÂ do {
> > > @@ -82,6 +86,9 @@ static void fpga_irq_handle(struct irq_desc *desc)
> > > ÂÂÂÂÂÂÂÂ status &= ~(1 << irq);
> > > ÂÂÂÂÂÂÂÂ generic_handle_irq(irq_find_mapping(f->domain, irq));
> > > ÂÂÂÂ } while (status);
> > > +
> > > +out:
> > > +ÂÂÂ chained_irq_exit(chip, desc);
> > > Â}
> > >
> > > Â/*
> >
> > 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?

Indeed, it has been broken forever. I'm tempted to say:

Fixes: c41b16f8c9d9d ("ARM: integrator/versatile: consolidate FPGA IRQ 
handling code")

even if it probably predates the introduction of the chained_irq_enter() 
helpers.
This will ensure this gets backported to older kernels...

Thanks,

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