linux-kernel - Re: [PATCH v3] irqchip/tango: Don't use incorrect irq_mask

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Date:   Wed, 26 Jul 2017 20:13:47 +0100
From:   Måns Rullgård <mans@...sr.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        Doug Berger <opendmb@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Jason Cooper <jason@...edaemon.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Mason <slash.tmp@...e.fr>
Subject: Re: [PATCH v3] irqchip/tango: Don't use incorrect irq_mask_ack callback

Florian Fainelli <f.fainelli@...il.com> writes:

> On 07/25/2017 06:29 AM, Måns Rullgård wrote:
>> Marc Gonzalez <marc_gonzalez@...madesigns.com> writes:
>> 
>>> On 25/07/2017 15:16, Måns Rullgård wrote:
>>>
>>>> What happened to the patch adding the proper combined function?
>>>
>>> It appears you're not CCed on v2.
>>>
>>> https://patchwork.kernel.org/patch/9859799/
>>>
>>> Doug wrote:
>>>> Yes, you understand correctly.  The irq_mask_ack method is entirely
>>>> optional and I assume that is why this issue went undetected for so
>>>> long; however, it is slightly more efficient to combine the functions
>>>> (even if the ack is unnecessary) which is why I chose to do so for my
>>>> changes to the irqchip-brcmstb-l2 driver where I first discovered this
>>>> issue.  How much value the improved efficiency has is certainly
>>>> debatable, but interrupt handling is one area where people might care
>>>> about such a small difference.  As the irqchip-tango driver maintainer
>>>> you are welcome to decide whether or not the irq_mask_ack method makes
>>>> sense to you.
>>>
>>> My preference goes to leaving the irq_mask_ack callback undefined,
>>> and let the irqchip framework use irq_mask and irq_ack instead.
>> 
>> Why would you prefer the less efficient way?
>> 
>
> Same question here, that does not really make sense to me.
>
> The whole point of this patch series is to have a set of efficient and
> bugfree (or nearly) helper functions that drivers can rely on, are you
> saying that somehow using irq_mask_and_ack is exposing a bug in the
> tango irqchip driver and using the separate functions does not expose
> this bug?

There is currently a bug in that the function used doesn't do what its
name implies which can't be good.  Using the separate mask and ack
functions obviously works, but combining them saves a lock/unlock
sequence.  The correct combined function has already been written, so I
see no reason not to use it.

-- 
Måns Rullgård