Re: [PATCH v2 2/6] irqchip/tango: Use irq_gc_mask_disable_and_ack_set

[Marc Gonzalez]

[ Trimming CC list ]

On 19/07/2017 21:07, Doug Berger wrote:

> From: Florian Fainelli <f.fainelli@xxxxxxxxx>
> 
> The only usage of the irq_gc_mask_disable_reg_and_ack() function
> is by the Tango irqchip driver. This usage is replaced by the
> irq_gc_mask_disable_and_ack_set() function since it provides the
> intended functionality.
> 
> Fixes: 4bba66899ac6 ("irqchip/tango: Add support for Sigma Designs SMP86xx/SMP87xx interrupt controller")
> Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> Acked-by: Mans Rullgard <mans@xxxxxxxxx>
> Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
> ---
>  drivers/irqchip/irq-tango.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-tango.c b/drivers/irqchip/irq-tango.c
> index bdbb5c0ff7fe..0c085303a583 100644
> --- a/drivers/irqchip/irq-tango.c
> +++ b/drivers/irqchip/irq-tango.c
> @@ -141,7 +141,7 @@ static void __init tangox_irq_init_chip(struct irq_chip_generic *gc,
>  	for (i = 0; i < 2; i++) {
>  		ct[i].chip.irq_ack = irq_gc_ack_set_bit;
>  		ct[i].chip.irq_mask = irq_gc_mask_disable_reg;
> -		ct[i].chip.irq_mask_ack = irq_gc_mask_disable_reg_and_ack;
> +		ct[i].chip.irq_mask_ack = irq_gc_mask_disable_and_ack_set;
>  		ct[i].chip.irq_unmask = irq_gc_unmask_enable_reg;
>  		ct[i].chip.irq_set_type = tangox_irq_set_type;
>  		ct[i].chip.name = gc->domain->name;
> 

(I had a look only at patches 1 and 2)

irq_gc_mask_disable_reg() =
	irq_reg_writel(gc, mask, ct->regs.disable);
	*ct->mask_cache &= ~mask;

irq_gc_ack_set_bit() =
	irq_reg_writel(gc, mask, ct->regs.ack);


irq_gc_mask_disable_reg_and_ack() =
	irq_reg_writel(gc, mask, ct->regs.mask);  // regs.mask not defined for tango driver
	irq_reg_writel(gc, mask, ct->regs.ack);

It will try to write at offset 0, which is a read-only register
so no disaster, but interrupt is not disabled. I wonder why
everything doesn't blow up...

irq_gc_mask_disable_and_ack_set() =
	irq_reg_writel(gc, mask, ct->regs.disable);
	*ct->mask_cache &= ~mask;
	irq_reg_writel(gc, mask, ct->regs.ack);


Your change makes sense.

But note that mask_ack_irq() is defined as:

static inline void mask_ack_irq(struct irq_desc *desc)
{
	if (desc->irq_data.chip->irq_mask_ack) {
		desc->irq_data.chip->irq_mask_ack(&desc->irq_data);
		irq_state_set_masked(desc);
	} else {
		mask_irq(desc);
		if (desc->irq_data.chip->irq_ack)
			desc->irq_data.chip->irq_ack(&desc->irq_data);
	}
}

So IIUC, if we don't define a irq_mask_ack() callback,
it will just call irq_mask() and irq_ack() which will
do the right thing.

So an alternative is simply to delete the assignment
of ct[i].chip.irq_mask_ack. What do you think?

diff --git a/drivers/irqchip/irq-tango.c b/drivers/irqchip/irq-tango.c
index bdbb5c0ff7fe..825085cdab99 100644
--- a/drivers/irqchip/irq-tango.c
+++ b/drivers/irqchip/irq-tango.c
@@ -141,7 +141,6 @@ static void __init tangox_irq_init_chip(struct irq_chip_generic *gc,
        for (i = 0; i < 2; i++) {
                ct[i].chip.irq_ack = irq_gc_ack_set_bit;
                ct[i].chip.irq_mask = irq_gc_mask_disable_reg;
-               ct[i].chip.irq_mask_ack = irq_gc_mask_disable_reg_and_ack;
                ct[i].chip.irq_unmask = irq_gc_unmask_enable_reg;
                ct[i].chip.irq_set_type = tangox_irq_set_type;
                ct[i].chip.name = gc->domain->name;


One thing I'm not sure about is why we need to ack for level
interrupts... We should be able to get away with defining ack()
only for edge interrupts... I'm confused. If I try to do that,
I get:

[    1.430547] irq 20: nobody cared (try booting with the "irqpoll" option)
[    1.437283] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.13.0-rc1 #148
[    1.443754] Hardware name: Sigma Tango DT
[    1.447812] [<c010e890>] (unwind_backtrace) from [<c010b01c>] (show_stack+0x10/0x14)
[    1.455598] [<c010b01c>] (show_stack) from [<c04a3fc4>] (dump_stack+0x84/0x98)
[    1.462864] [<c04a3fc4>] (dump_stack) from [<c0159d80>] (__report_bad_irq+0x28/0xcc)
[    1.470650] [<c0159d80>] (__report_bad_irq) from [<c015a188>] (note_interrupt+0x28c/0x2dc)
[    1.478959] [<c015a188>] (note_interrupt) from [<c0157688>] (handle_irq_event_percpu+0x4c/0x58)
[    1.487702] [<c0157688>] (handle_irq_event_percpu) from [<c01576cc>] (handle_irq_event+0x38/0x5c)
[    1.496621] [<c01576cc>] (handle_irq_event) from [<c015aa84>] (handle_level_irq+0xa8/0x124)
[    1.505017] [<c015aa84>] (handle_level_irq) from [<c01568bc>] (generic_handle_irq+0x24/0x34)
[    1.513501] [<c01568bc>] (generic_handle_irq) from [<c02f9dc0>] (tangox_dispatch_irqs+0x4c/0x58)
[    1.522333] [<c02f9dc0>] (tangox_dispatch_irqs) from [<c02f9e18>] (tangox_irq_handler+0x4c/0xb0)
[    1.531163] [<c02f9e18>] (tangox_irq_handler) from [<c01568bc>] (generic_handle_irq+0x24/0x34)
[    1.539819] [<c01568bc>] (generic_handle_irq) from [<c0156df4>] (__handle_domain_irq+0x5c/0xb4)
[    1.548562] [<c0156df4>] (__handle_domain_irq) from [<c0101450>] (gic_handle_irq+0x48/0x8c)
[    1.556956] [<c0101450>] (gic_handle_irq) from [<c010bb4c>] (__irq_svc+0x6c/0xa8)


Regards.