linux-kernel - Re: [PATCH v2 1/2] genirq: add an irq_create_mapping

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Date:   Wed, 25 Nov 2020 16:00:03 +0100
From:   Laurent Vivier <lvivier@...hat.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        linux-pci@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        "Michael S . Tsirkin" <mst@...hat.com>, Greg Kurz <groug@...d.org>,
        Christoph Hellwig <hch@....de>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v2 1/2] genirq: add an irq_create_mapping_affinity()
 function

On 25/11/2020 15:54, Marc Zyngier wrote:
> On 2020-11-25 14:09, Laurent Vivier wrote:
>> On 25/11/2020 14:20, Thomas Gleixner wrote:
>>> Laurent,
>>>
>>> On Wed, Nov 25 2020 at 12:16, Laurent Vivier wrote:
>>>
>>> The proper subsystem prefix is: 'genirq/irqdomain:' and the first letter
>>> after the colon wants to be uppercase.
>>
>> Ok.
>>
>>>> This function adds an affinity parameter to irq_create_mapping().
>>>> This parameter is needed to pass it to irq_domain_alloc_descs().
>>>
>>> A changelog has to explain the WHY. 'The parameter is needed' is not
>>> really useful information.
>>>
>>
>> The reason of this change is explained in PATCH 2.
>>
>> I have two patches, one to change the interface with no functional
>> change (PATCH 1) and
>> one to fix the problem (PATCH 2). Moreover they don't cover the same subsystems.
>>
>> I can either:
>> - merge the two patches
>> - or make a reference in the changelog of PATCH 1 to PATCH 2
>>   (something like "(see folowing patch "powerpc/pseries: pass MSI affinity to
>>    irq_create_mapping()")")
>> - or copy some information from PATCH 2
>>   (something like "this parameter is needed by rtas_setup_msi_irqs()
>> to pass the affinity
>>    to irq_domain_alloc_descs() to fix multiqueue affinity")
>>
>> What do you prefer?
> 
> How about something like this for the first patch:
> 
> "There is currently no way to convey the affinity of an interrupt
>  via irq_create_mapping(), which creates issues for devices that
>  expect that affinity to be managed by the kernel.
> 
>  In order to sort this out, rename irq_create_mapping() to
>  irq_create_mapping_affinity() with an additional affinity parameter
>  that can conveniently passed down to irq_domain_alloc_descs().
> 
>  irq_create_mapping() is then re-implemented as a wrapper around
>  irq_create_mapping_affinity()."

It looks perfect. I update the changelog with that.

Thanks,
Laurent