linux-kernel - Re: [PATCH] irqchip/irq-brcmstb-l2: add write memory barrier before exit

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Date: Tue, 9 Jan 2024 15:05:12 -0800
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Doug Berger <opendmb@...il.com>, Thomas Gleixner <tglx@...utronix.de>
Cc: bcm-kernel-feedback-list@...adcom.com, linux-mips@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] irqchip/irq-brcmstb-l2: add write memory barrier before
 exit

On 12/21/23 03:14, Florian Fainelli wrote:
> 
> 
> On 12/20/2023 8:32 PM, Doug Berger wrote:
>> It was observed on Broadcom devices that use GIC v3 architecture
>> L1 interrupt controllers as the parent of brcmstb-l2 interrupt
>> controllers that the deactivation of the parent irq could happen
>> before the brcmstb-l2 deasserted its output. This would lead the
>> GIC to reactivate the irq only to find that no L2 interrupt was
>> pending. The result was a spurious interrupt invoking the
>> handle_bad_irq() with its associated messaging. While this did
>> not create a functional problem it is a waste of cycles.
>>
>> The hazard exists because the memory mapped bus writes to the
>> brcmstb-l2 registers are buffered and the GIC v3 architecture
>> uses a very efficient system register write to deactivate the
>> interrupt. This commit adds a write memory barrier prior to
>> invoking chained_irq_exit() to introduce a dsb(st) on those
>> systems to ensure the system register write cannot be executed
>> until the memory mapped writes are visible to the system.
>>
>> Signed-off-by: Doug Berger <opendmb@...il.com>
> 
> Acked-by: Florian Fainelli <florian.fainelli@...adcom.com>
> 
> I would be even keen on slapping a:
> 
> Fixes: 7f646e92766e ("irqchip: brcmstb-l2: Add Broadcom Set Top Box 
> Level-2 interrupt controller")
> 
> Thanks Doug!

Thomas, are you able to apply Doug's patch including the Fixes tag, or 
do you need it to be re-submitted with that tag as well as my Acked-by?

Thanks!
-- 
Florian


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