linux-kernel - Re: [PATCH v3 5/5] irqchip: gicv3-its: support safe initialization

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Date:	Thu, 05 Mar 2015 12:05:33 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Yun Wu <wuyun.wu@...wei.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"jason@...edaemon.net" <jason@...edaemon.net>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 5/5] irqchip: gicv3-its: support safe initialization

On 04/03/15 03:18, Yun Wu wrote:
> It's unsafe to change the configurations of an activated ITS directly
> since this will lead to unpredictable results. This patch guarantees
> the ITSes being initialized are quiescent.
> 
> Signed-off-by: Yun Wu <wuyun.wu@...wei.com>
> ---
>  drivers/irqchip/irq-gic-v3-its.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index d13c24e..9e09aa0 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -1320,6 +1320,34 @@ static const struct irq_domain_ops its_domain_ops = {
>  	.deactivate		= its_irq_domain_deactivate,
>  };
> 
> +static int its_check_quiesced(void __iomem *base)

Another nitpick: Rather than "its_check_quiesced", how about
"its_force_quiescent" instead? Because this does a lot more than just
checking.

> +{
> +	u32 count = 1000000;	/* 1s */
> +	u32 val;
> +
> +	val = readl_relaxed(base + GITS_CTLR);
> +	if (val & GITS_CTLR_QUIESCENT)
> +		return 0;
> +
> +	/* Disable the generation of all interrupts to this ITS */
> +	val &= ~GITS_CTLR_ENABLE;
> +	writel_relaxed(val, base + GITS_CTLR);
> +
> +	/* Poll GITS_CTLR and wait until ITS becomes quiescent */
> +	while (1) {
> +		val = readl_relaxed(base + GITS_CTLR);
> +		if (val & GITS_CTLR_QUIESCENT)
> +			return 0;
> +
> +		count--;
> +		if (!count)
> +			return -EBUSY;
> +
> +		cpu_relax();
> +		udelay(1);
> +	}
> +}
> +

I still dislike this repeated pattern, but I don't have a good solution
so far.

>  static int its_probe(struct device_node *node, struct irq_domain *parent)
>  {
>  	struct resource res;
> @@ -1348,6 +1376,13 @@ static int its_probe(struct device_node *node, struct irq_domain *parent)
>  		goto out_unmap;
>  	}
> 
> +	err = its_check_quiesced(its_base);
> +	if (err) {
> +		pr_warn("%s: failed to quiesce, giving up\n",
> +			node->full_name);
> +		goto out_unmap;
> +	}
> +
>  	pr_info("ITS: %s\n", node->full_name);
> 
>  	its = kzalloc(sizeof(*its), GFP_KERNEL);
> --
> 1.8.0
> 
> 
> 

Assuming you fix the above nitpick:

Acked-by: Marc Zyngier <marc.zyngier@....com>

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