linux-kernel - Re: [RFC PATCH v4 18/21] x86/apic: Add a parameter for the APIC delivery mode

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Date:   Tue, 18 Jun 2019 15:47:38 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Ashok Raj <ashok.raj@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Andi Kleen <andi.kleen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Stephane Eranian <eranian@...gle.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Ricardo Neri <ricardo.neri@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Juergen Gross <jgross@...e.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Wincy Van <fanwenyi0529@...il.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Baoquan He <bhe@...hat.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: Re: [RFC PATCH v4 18/21] x86/apic: Add a parameter for the APIC
 delivery mode

On Sun, Jun 16, 2019 at 11:55:03AM +0200, Thomas Gleixner wrote:
> On Thu, 23 May 2019, Ricardo Neri wrote:
> >  
> >  struct irq_cfg {
> > -	unsigned int		dest_apicid;
> > -	unsigned int		vector;
> > +	unsigned int				dest_apicid;
> > +	unsigned int				vector;
> > +	enum ioapic_irq_destination_types	delivery_mode;
> 
> And how is this related to IOAPIC?

In my view, IOAPICs can also be programmed with a delivery mode. Mode
values are the same for MSI interrupts.

> I know this enum exists already, but in
> connection with MSI this does not make any sense at all.

Is the issue here the name of the enumeration?

> 
> > +
> > +		/*
> > +		 * Initialize the delivery mode of this irq to match the
> > +		 * default delivery mode of the APIC. This is useful for
> > +		 * children irq domains which want to take the delivery
> > +		 * mode from the individual irq configuration rather
> > +		 * than from the APIC.
> > +		 */
> > +		 apicd->hw_irq_cfg.delivery_mode = apic->irq_delivery_mode;
> 
> And here it's initialized from apic->irq_delivery_mode, which is an
> u32. Intuitive and consistent - NOT!

Yes, this is wrong. Then should the member in the structure above be an
u32 instead of enum ioapic_irq_destination_types?

Thanks and BR,
Ricardo