Re: [PATCH v6 03/29] x86/apic/msi: Set the delivery mode individually for each IRQ

From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
	Ricardo Neri <ricardo.neri@intel.com>,
	Stephane Eranian <eranian@google.com>,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	Tony Luck <tony.luck@intel.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH v6 03/29] x86/apic/msi: Set the delivery mode individually for each IRQ
Date: Wed, 11 May 2022 17:38:45 -0700	[thread overview]
Message-ID: <20220512003845.GC16273@ranerica-svr.sc.intel.com> (raw)
In-Reply-To: <8735hmh1f5.ffs@tglx>

On Fri, May 06, 2022 at 10:05:34PM +0200, Thomas Gleixner wrote:
> On Thu, May 05 2022 at 16:59, Ricardo Neri wrote:
> > There are no restrictions in hardware to set  MSI messages with its
> > own delivery mode.
> 
> "messages with its own" ? Plural/singular confusion.

Yes, this is not correct. It should have read "messages with their own..."

> 
> > Use the mode specified in the provided IRQ hardware
> > configuration data. Since most of the IRQs are configured to use the
> > delivery mode of the APIC driver in use (set in all of them to
> > APIC_DELIVERY_MODE_FIXED), the only functional changes are where
> > IRQs are configured to use a specific delivery mode.
> 
> This does not parse. There are no functional changes due to this patch
> and there is no point talking about functional changes in subsequent
> patches here.

I will remove this.

> 
> > Changing the utility function __irq_msi_compose_msg() takes care of
> > implementing the change in the in the local APIC, PCI-MSI, and DMAR-MSI
> 
> in the in the

Sorry! This is not correct.

> 
> > irq_chips.
> >
> > The IO-APIC irq_chip configures the entries in the interrupt redirection
> > table using the delivery mode specified in the corresponding MSI message.
> > Since the MSI message is composed by a higher irq_chip in the hierarchy,
> > it does not need to be updated.
> 
> The point is that updating __irq_msi_compose_msg() covers _all_ MSI
> consumers including IO-APIC.
> 
> I had to read that changelog 3 times to make sense of it. Something like
> this perhaps:
> 
>   "x86/apic/msi: Use the delivery mode from irq_cfg for message composition
> 
>    irq_cfg provides a delivery mode for each interrupt. Use it instead
>    of the hardcoded APIC_DELIVERY_MODE_FIXED. This allows to compose
>    messages for NMI delivery mode which is required to implement a HPET
>    based NMI watchdog.
> 
>    No functional change as the default delivery mode is set to
>    APIC_DELIVERY_MODE_FIXED."

Thank you for your help on the changelog! I will take your suggestion.

BR,
Ricardo
> 
> Thanks,
> 
>         tglx
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