linux-kernel - Re: [PATCH v2 2/6] KVM: arm/arm64: arch_timer: Rely on the arch timer to parse the firmware tables

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Date:	Thu, 3 Mar 2016 20:38:08 +0100
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Julien Grall <julien.grall@....com>
Cc:	kvmarm@...ts.cs.columbia.edu, marc.zyngier@....com,
	fu.wei@...aro.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	wei@...hat.com, al.stone@...aro.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 2/6] KVM: arm/arm64: arch_timer: Rely on the arch
 timer to parse the firmware tables

On Thu, Feb 11, 2016 at 03:33:20PM +0000, Julien Grall wrote:
> The firmware table is currently parsed by the virt timer code in order
> to retrieve the virtual interrupt. However, this is already done by the
> arch timer driver and therefore make the parsing code duplicated twice.
> 
> Introduce an helper to get the virtual interrupt number and use it in
> the virtual timer code.
> 
> With this changes, the support for ACPI is coming free.
> 
> Signed-off-by: Julien Grall <julien.grall@....com>
> 
> ---
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Christoffer Dall <christoffer.dall@...aro.org>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Gleb Natapov <gleb@...nel.org>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  drivers/clocksource/arm_arch_timer.c |  2 ++
>  include/clocksource/arm_arch_timer.h |  1 +
>  virt/kvm/arm/arch_timer.c            | 33 +++++++--------------------------
>  3 files changed, 10 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 6eb2c5d..3cdbefd 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -451,6 +451,8 @@ static struct arch_timer_kvm_info arch_timer_kvm_info;
>  
>  struct arch_timer_kvm_info *arch_timer_get_kvm_info(void)
>  {
> +	arch_timer_kvm_info.virtual_irq = arch_timer_ppi[VIRT_PPI];
> +

it feels weird that we set this member on every retrieval of the pointer
to the struct?

wouldn't it be more natural to intialize the struct somewhere during
init and then this function just returns a pointer to the struct?

>  	return &arch_timer_kvm_info;
>  }
>  
> diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
> index 4d487f8..8890552 100644
> --- a/include/clocksource/arm_arch_timer.h
> +++ b/include/clocksource/arm_arch_timer.h
> @@ -51,6 +51,7 @@ enum arch_timer_reg {
>  
>  struct arch_timer_kvm_info {
>  	struct timecounter timecounter;
> +	int virtual_irq;
>  };
>  
>  #ifdef CONFIG_ARM_ARCH_TIMER
> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> index a669c6a..e4de549 100644
> --- a/virt/kvm/arm/arch_timer.c
> +++ b/virt/kvm/arm/arch_timer.c
> @@ -17,7 +17,6 @@
>   */
>  
>  #include <linux/cpu.h>
> -#include <linux/of_irq.h>
>  #include <linux/kvm.h>
>  #include <linux/kvm_host.h>
>  #include <linux/interrupt.h>
> @@ -375,45 +374,28 @@ static struct notifier_block kvm_timer_cpu_nb = {
>  	.notifier_call = kvm_timer_cpu_notify,
>  };
>  
> -static const struct of_device_id arch_timer_of_match[] = {
> -	{ .compatible	= "arm,armv7-timer",	},
> -	{ .compatible	= "arm,armv8-timer",	},
> -	{},
> -};
> -
>  int kvm_timer_hyp_init(void)
>  {
> -	struct device_node *np;
> -	unsigned int ppi;
>  	struct arch_timer_kvm_info *info;
>  	int err;
>  
>  	info = arch_timer_get_kvm_info();
>  	timecounter = &info->timecounter;
>  
> -	np = of_find_matching_node(NULL, arch_timer_of_match);
> -	if (!np) {
> -		kvm_err("kvm_arch_timer: can't find DT node\n");
> +	host_vtimer_irq = info->virtual_irq;
> +	if (host_vtimer_irq <= 0) {
> +		kvm_err("kvm_arch_timer: can't find virtual timer info or config virtual timer interrupt\n");

I don't understand the difference between the two cases in this error
message.

How about: "Invalid virtual timer IRQ: %d\n" ?

>  		return -ENODEV;
>  	}
>  
> -	ppi = irq_of_parse_and_map(np, 2);
> -	if (!ppi) {
> -		kvm_err("kvm_arch_timer: no virtual timer interrupt\n");
> -		err = -EINVAL;
> -		goto out;
> -	}
> -
> -	err = request_percpu_irq(ppi, kvm_arch_timer_handler,
> +	err = request_percpu_irq(host_vtimer_irq, kvm_arch_timer_handler,
>  				 "kvm guest timer", kvm_get_running_vcpus());
>  	if (err) {
>  		kvm_err("kvm_arch_timer: can't request interrupt %d (%d)\n",
> -			ppi, err);
> +			host_vtimer_irq, err);
>  		goto out;
>  	}
>  
> -	host_vtimer_irq = ppi;
> -
>  	err = __register_cpu_notifier(&kvm_timer_cpu_nb);
>  	if (err) {
>  		kvm_err("Cannot register timer CPU notifier\n");
> @@ -426,14 +408,13 @@ int kvm_timer_hyp_init(void)
>  		goto out_free;
>  	}
>  
> -	kvm_info("%s IRQ%d\n", np->name, ppi);
> +	kvm_info("vtimer IRQ%d\n", host_vtimer_irq);

is "vtimer" a known concept anywhere?  If not, can you use some known
terms intead?

>  	on_each_cpu(kvm_timer_init_interrupt, NULL, 1);
>  
>  	goto out;
>  out_free:
> -	free_percpu_irq(ppi, kvm_get_running_vcpus());
> +	free_percpu_irq(host_vtimer_irq, kvm_get_running_vcpus());
>  out:
> -	of_node_put(np);
>  	return err;
>  }
>  
> -- 
> 1.9.1
> 

Thanks,
-Christoffer