linux-kernel - Re: [PATCH] irqchip: gic-v3: Handle failure case of CPU enters low power state

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Message-ID: <86bknnbx18.wl-maz@kernel.org>
Date:   Wed, 28 Dec 2022 11:14:11 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Pavan Kondeti <quic_pkondeti@...cinc.com>
Cc:     Yogesh Lal <quic_ylal@...cinc.com>, <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH] irqchip: gic-v3: Handle failure case of CPU enters low power state

On Tue, 27 Dec 2022 10:36:38 +0000,
Pavan Kondeti <quic_pkondeti@...cinc.com> wrote:
> 
> Hi Yogesh,
> 
> On Fri, Dec 23, 2022 at 12:05:40AM +0530, Yogesh Lal wrote:
> > When CPU enter in low power mode it disable the redistributor and
> > Group1 interrupts. And re-initialise the system registers on wakeup.
> > 
> > But in case of failure to enter low power mode need to enable
> > the redistributor and Group1 interrupts.
> > 
> > Signed-off-by: Yogesh Lal <quic_ylal@...cinc.com>
> > ---
> >  drivers/irqchip/irq-gic-v3.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> > index 997104d..4904f00 100644
> > --- a/drivers/irqchip/irq-gic-v3.c
> > +++ b/drivers/irqchip/irq-gic-v3.c
> > @@ -1376,7 +1376,7 @@ static int gic_retrigger(struct irq_data *data)
> >  static int gic_cpu_pm_notifier(struct notifier_block *self,
> >  			       unsigned long cmd, void *v)
> >  {
> > -	if (cmd == CPU_PM_EXIT) {
> > +	if (cmd == CPU_PM_EXIT || cmd == CPU_PM_ENTER_FAILED) {
> >  		if (gic_dist_security_disabled())
> >  			gic_enable_redist(true);
> >  		gic_cpu_sys_reg_init();
> 
> static int gic_cpu_pm_notifier(struct notifier_block *self,
> 			       unsigned long cmd, void *v)
> {
> 	if (cmd == CPU_PM_EXIT) {
> 		if (gic_dist_security_disabled())
> 			gic_enable_redist(true);
> 		gic_cpu_sys_reg_init();
> 	} else if (cmd == CPU_PM_ENTER && gic_dist_security_disabled()) {
> 		gic_write_grpen1(0);
> 		gic_enable_redist(false);
> 	}
> 	return NOTIFY_OK;
> }
> 
> During CPU_PM_ENTER notification, we are not doing anything for the
> !gic_dist_security_disabled() case. Since CPU_PM_ENTER_FAILED notification
> arrive when CPU fails to power down, do we need to reinitialize the
> system registers? IOW, should we do different handling for CPU_PM_ENTER_FAILED
> based on gic_dist_security_disabled()?

What does it gain you apart from the extra complexity?

gic_cpu_sys_reg_init() does very little, and makes sure we're always
back into a sane state.

	M.

-- 
Without deviation from the norm, progress is not possible.