linux-kernel - Re: [PATCH 3/5] irqchip/bcm2836: Make IPIs use handle_percpu_devid

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Date:   Tue, 15 Dec 2020 11:14:50 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, Andrew Lunn <andrew@...n.ch>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Jason Cooper <jason@...edaemon.net>,
        Scott Branden <sbranden@...adcom.com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 3/5] irqchip/bcm2836: Make IPIs use handle_percpu_devid_irq()


On 15/12/20 10:19, Marc Zyngier wrote:
> Hi Gunter,
>
> On 2020-12-15 00:21, Guenter Roeck wrote:
>> On Mon, Nov 09, 2020 at 09:41:19AM +0000, Valentin Schneider wrote:
>>> As done for the Arm GIC irqchips, move IPIs to
>>> handle_percpu_devid_irq() as
>>> handle_percpu_devid_fasteoi_ipi() isn't actually required.
>>>
>>> Signed-off-by: Valentin Schneider <valentin.schneider@....com>
>>
>> This patch results in boot failures (silent stall) for the qemu
>> raspi2 emulation. Unfortunately it can not be reverted because
>> handle_percpu_devid_fasteoi_ipi no longer exists in next-20201214,
>> so I don't know if it is the only problem.
>
> This is odd. This works just fine for me on both the RPi2 and 3
> emulation, running a full Debian userspace. Could this be caused
> by the version of QEMU you are using? Here's what I have:
>
> $ qemu-system-arm --version
> QEMU emulator version 5.1.0 (Debian 1:5.1+dfsg-4+b1)
>
> Could you try the following hack and let me know if that helps?
>

Thanks for looking into this. It does look like I inverted the ordering of
that mailbox write vs the handling of the IPI. I don't see how the IPI
could mess with the mailbox (unless some creative use of irq_work /
smp_call), but in any case having the write in irq_ack() as you've done
below should restore said ordering.

> Thanks,
>
>          M.
>
> diff --git a/drivers/irqchip/irq-bcm2836.c
> b/drivers/irqchip/irq-bcm2836.c
> index 5f5eb8877c41..25c9a9c06e41 100644
> --- a/drivers/irqchip/irq-bcm2836.c
> +++ b/drivers/irqchip/irq-bcm2836.c
> @@ -167,7 +167,7 @@ static void bcm2836_arm_irqchip_handle_ipi(struct
> irq_desc *desc)
>       chained_irq_exit(chip, desc);
>   }
>
> -static void bcm2836_arm_irqchip_ipi_eoi(struct irq_data *d)
> +static void bcm2836_arm_irqchip_ipi_ack(struct irq_data *d)
>   {
>       int cpu = smp_processor_id();
>
> @@ -195,7 +195,7 @@ static struct irq_chip bcm2836_arm_irqchip_ipi = {
>       .name		= "IPI",
>       .irq_mask	= bcm2836_arm_irqchip_dummy_op,
>       .irq_unmask	= bcm2836_arm_irqchip_dummy_op,
> -	.irq_eoi	= bcm2836_arm_irqchip_ipi_eoi,
> +	.irq_ack	= bcm2836_arm_irqchip_ipi_ack,
>       .ipi_send_mask	= bcm2836_arm_irqchip_ipi_send_mask,
>   };