linux-kernel - Re: [PATCH] PCI: altera-msi: Remove irq handler and data in one go

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Message-ID: <87h7pumo9l.fsf@nanos.tec.linutronix.de>
Date:   Thu, 12 Nov 2020 19:19:18 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Martin Kaiser <martin@...ser.cx>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        rfi@...ts.rocketboards.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Toan Le <toan@...amperecomputing.com>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH] PCI: altera-msi: Remove irq handler and data in one go

On Thu, Nov 12 2020 at 08:26, Bjorn Helgaas wrote:
> On Thu, Nov 12, 2020 at 02:50:42PM +0100, Thomas Gleixner wrote:
>> So I had a closer look and the reason why it only matters for the
>> chained handler case is that
>> 
>>    __irq_set_handler(..., is_chained = true, ...)
>> 
>> starts up the interrupt immediately. So the order for this _must_ be:
>> 
>>     set_handler_data() -> set_handler()
>> 
>> For regular interrupts it's really the mapping and allocation code which
>> does this long before the interrupt is started up. So the ordering does
>> not matter because the handler can't be reached before the full
>> setup is finished and the interrupt is actually started up.
>
> If the order truly doesn't matter here, maybe it's worth changing it
> to "set data, set handler" to avoid the need for a closer look to
> verify correctness and to make it harder to copy and paste to a place
> where it *does* matter?

Makes sense.