Re: [PATCH v2] irqchip/bcm2835: Quiesce IRQs left enabled by bootloader

[Nicolas Saenz Julienne]

On Wed, 2020-02-12 at 13:36 +0100, Lukas Wunner wrote:
> On Tue, Feb 11, 2020 at 08:47:05PM -0800, Florian Fainelli wrote:
> > The commit message is a bit long and starts
> > going into details that I am not sure add anything
> 
> I adhere to the school of thought which holds that commit messages
> shall provide complete context, including numbers to back up claims,
> user-visible impact, affected versions, genesis of the fix and so on.
> By that logic there's no such a thing as a too long commit message.
> 
> Nevertheless please find a shortened version below, complete with
> the Fixes tag you requested as well as your R-b.
> 
> 
> On Wed, Feb 12, 2020 at 08:13:29AM +0000, Marc Zyngier wrote:
> > It otherwise looks good. You can either resend it with a fixed commit
> > message,
> > or provide me with a commit message that I can stick there while applying
> > it.
> 
> The below also contains the patch itself, so can be applied directly
> with git am --scissors.  Feel free to tweak as you see fit.
> Shout if I've missed anything.  Thanks.
> 
> -- >8 --
> From: Lukas Wunner <lukas@xxxxxxxxx>
> Subject: [PATCH] irqchip/bcm2835: Quiesce IRQs left enabled by bootloader
> 
> Per the spec, the BCM2835's IRQs are all disabled when coming out of
> power-on reset.  Its IRQ driver assumes that's still the case when the
> kernel boots and does not perform any initialization of the registers.
> However the Raspberry Pi Foundation's bootloader leaves the USB
> interrupt enabled when handing over control to the kernel.
> 
> Quiesce IRQs and the FIQ if they were left enabled and log a message to
> let users know that they should update the bootloader once a fixed
> version is released.
> 
> If the USB interrupt is not quiesced and the USB driver later on claims
> the FIQ (as it does on the Raspberry Pi Foundation's downstream kernel),
> interrupt latency for all other peripherals increases and occasional
> lockups occur.  That's because both the FIQ and the normal USB interrupt
> fire simultaneously.
> 
> On a multicore Raspberry Pi, if normal interrupts are routed to CPU 0
> and the FIQ to CPU 1 (hardcoded in the Foundation's kernel), then a USB
> interrupt causes CPU 0 to spin in bcm2836_chained_handle_irq() until the
> FIQ on CPU 1 has cleared it.  Other peripherals' interrupts are starved
> as long.  I've seen CPU 0 blocked for up to 2.9 msec.  eMMC throughput
> on a Compute Module 3 irregularly dips to 23.0 MB/s without this commit
> but remains relatively constant at 23.5 MB/s with this commit.
> 
> The lockups occur when CPU 0 receives a USB interrupt while holding a
> lock which CPU 1 is trying to acquire while the FIQ is temporarily
> disabled on CPU 1.  At best users get RCU CPU stall warnings, but most
> of the time the system just freezes.
> 
> Fixes: 89214f009c1d ("ARM: bcm2835: add interrupt controller driver")
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> Reviewed-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v3.7+
> Cc: Serge Schneider <serge@xxxxxxxxxxxxxxx>
> Cc: Kristina Brooks <notstina@xxxxxxxxx>

Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>

Thanks!

> ---
>  drivers/irqchip/irq-bcm2835.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/irqchip/irq-bcm2835.c b/drivers/irqchip/irq-bcm2835.c
> index 418245d..eca9ac7 100644
> --- a/drivers/irqchip/irq-bcm2835.c
> +++ b/drivers/irqchip/irq-bcm2835.c
> @@ -135,6 +135,7 @@ static int __init armctrl_of_init(struct device_node
> *node,
>  {
>  	void __iomem *base;
>  	int irq, b, i;
> +	u32 reg;
>  
>  	base = of_iomap(node, 0);
>  	if (!base)
> @@ -157,6 +158,19 @@ static int __init armctrl_of_init(struct device_node
> *node,
>  				handle_level_irq);
>  			irq_set_probe(irq);
>  		}
> +
> +		reg = readl_relaxed(intc.enable[b]);
> +		if (reg) {
> +			writel_relaxed(reg, intc.disable[b]);
> +			pr_err(FW_BUG "Bootloader left irq enabled: "
> +			       "bank %d irq %*pbl\n", b, IRQS_PER_BANK, &reg);
> +		}
> +	}
> +
> +	reg = readl_relaxed(base + REG_FIQ_CONTROL);
> +	if (reg & REG_FIQ_ENABLE) {
> +		writel_relaxed(0, base + REG_FIQ_CONTROL);
> +		pr_err(FW_BUG "Bootloader left fiq enabled\n");
>  	}
>  
>  	if (is_2836) {

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