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

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Message-ID: <5100171ff6d4c3efffe008e1e0bf3707@kernel.org>
Date:   Wed, 25 Nov 2020 14:54:21 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Laurent Vivier <lvivier@...hat.com>
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 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()."

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...