linux-kernel - Re: [PATCH v1] irqchip/irq-sifive-plic: Add syscore callbacks for hibernation

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Message-ID: <21d774af-76bb-538e-b0f6-f52295116fa7@starfivetech.com>
Date:   Tue, 7 Feb 2023 11:50:35 +0800
From:   Mason Huo <mason.huo@...rfivetech.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        <linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
        Ley Foon Tan <leyfoon.tan@...rfivetech.com>,
        Sia Jee Heng <jeeheng.sia@...rfivetech.com>
Subject: Re: [PATCH v1] irqchip/irq-sifive-plic: Add syscore callbacks for
 hibernation



On 2023/2/6 20:48, Marc Zyngier wrote:
> On Mon, 06 Feb 2023 06:13:11 +0000,
> Mason Huo <mason.huo@...rfivetech.com> wrote:
>> 
>> 
>> 
>> On 2023/2/5 18:51, Marc Zyngier wrote:
>> > On Fri, 13 Jan 2023 09:42:16 +0000,
>> > Mason Huo <mason.huo@...rfivetech.com> wrote:
>> >> 
>> >> The priority and enable registers of plic will be reset
>> >> during hibernation power cycle in poweroff mode,
>> >> add the syscore callbacks to save/restore those registers.
>> >> 
>> >> Signed-off-by: Mason Huo <mason.huo@...rfivetech.com>
>> >> Reviewed-by: Ley Foon Tan <leyfoon.tan@...rfivetech.com>
>> >> Reviewed-by: Sia Jee Heng <jeeheng.sia@...rfivetech.com>
>> >> ---
>> >>  drivers/irqchip/irq-sifive-plic.c | 93 ++++++++++++++++++++++++++++++-
>> >>  1 file changed, 91 insertions(+), 2 deletions(-)
>> >> 
>> >> diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
>> >> index ff47bd0dec45..80306de45d2b 100644
>> >> --- a/drivers/irqchip/irq-sifive-plic.c
>> >> +++ b/drivers/irqchip/irq-sifive-plic.c
>> >> @@ -17,6 +17,7 @@
>> >>  #include <linux/of_irq.h>
>> >>  #include <linux/platform_device.h>
>> >>  #include <linux/spinlock.h>
>> >> +#include <linux/syscore_ops.h>
>> >>  #include <asm/smp.h>
>> >>  
>> >>  /*
>> >> @@ -67,6 +68,8 @@ struct plic_priv {
>> >>  	struct irq_domain *irqdomain;
>> >>  	void __iomem *regs;
>> >>  	unsigned long plic_quirks;
>> >> +	unsigned int nr_irqs;
>> >> +	u32 *priority_reg;
>> >>  };
>> >>  
>> >>  struct plic_handler {
>> >> @@ -79,10 +82,13 @@ struct plic_handler {
>> >>  	raw_spinlock_t		enable_lock;
>> >>  	void __iomem		*enable_base;
>> >>  	struct plic_priv	*priv;
>> >> +	/* To record interrupts that are enabled before suspend. */
>> >> +	u32 enable_reg[MAX_DEVICES / 32];
>> > 
>> > What does MAX_DEVICES represent here? How is it related to the number
>> > of interrupts you're trying to save? It seems to be related to the
>> > number of CPUs, so it hardly makes any sense so far.
>> > 
>> The comment of this macro describes that "The largest number supported
>> by devices marked as 'sifive,plic-1.0.0', is 1024, of which
>> device 0 is defined as non-existent by the RISC-V Privileged Spec."
>> As far as I understand, the *device* here means HW IRQ source,
>> and the HW IRQ 0 is non-existent.
> 
> So why is it sized to that maximum value? The binding gives you the
> *real* value that the HW implements.
> 
OK, will change to use binding value.

>> 
>> >>  };
>> >>  static int plic_parent_irq __ro_after_init;
>> >>  static bool plic_cpuhp_setup_done __ro_after_init;
>> >>  static DEFINE_PER_CPU(struct plic_handler, plic_handlers);
>> >> +static struct plic_priv *priv_data;
>> >>  
>> >>  static int plic_irq_set_type(struct irq_data *d, unsigned int type);
>> >>  
>> >> @@ -229,6 +235,78 @@ static int plic_irq_set_type(struct irq_data *d, unsigned int type)
>> >>  	return IRQ_SET_MASK_OK;
>> >>  }
>> >>  
>> >> +static void plic_irq_resume(void)
>> >> +{
>> >> +	unsigned int i, cpu;
>> >> +	u32 __iomem *reg;
>> >> +
>> >> +	for (i = 0; i < priv_data->nr_irqs; i++)
>> >> +		writel(priv_data->priority_reg[i],
>> >> +				priv_data->regs + PRIORITY_BASE + i * PRIORITY_PER_ID);
>> > 
>> > From what I can tell, this driver uses exactly 2 priorities: 0 and 1.
>> > And yet you use a full 32bit to encode those. Does it seem like a good
>> > idea?
>> > 
>> Yes, currently this driver uses oly 2 priorities.
>> But, according to the sifive spec, the priority register is a 32bit register,
>> and it supports 7 levels of priority.
> 
> And? This is a Linux driver, not an implementation validation
> tool. What is the point of saving/restoring stuff that is *never*
> used? :-(
> 
> 	M.
> OK, will save/restore the priority in 1 bit. 

Thanks
Mason