linux-kernel - Re: [PATCH] x86/apic: Update virtual irq base for DT/OF based system as well

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Message-ID: <alpine.DEB.2.21.1908211028030.2223@nanos.tec.linutronix.de>
Date:   Wed, 21 Aug 2019 10:34:55 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Rahul Tanwar <rahul.tanwar@...ux.intel.com>
cc:     mingo@...hat.com, bp@...en8.de, hpa@...or.com, tony.luck@...el.com,
        x86@...nel.org, andriy.shevchenko@...el.com, alan@...ux.intel.com,
        rppt@...ux.ibm.com, linux-kernel@...r.kernel.org,
        qi-ming.wu@...el.com, cheol.yong.kim@...el.com,
        rahul.tanwar@...el.com
Subject: Re: [PATCH] x86/apic: Update virtual irq base for DT/OF based system
 as well

On Wed, 21 Aug 2019, Rahul Tanwar wrote:

> 'ioapic_dynirq_base' contains the virtual IRQ base number. Presently, it is
> updated to the end of hardware IRQ numbers but this is done only when IOAPIC
> configuration type is IOAPIC_DOMAIN_LEGACY or IOAPIC_DOMAIN_STRICT. There is
> a third type IOAPIC_DOMAIN_DYNAMIC which applies when IOAPIC configuration
> comes from devicetree.
> Please see dtb_add_ioapic() in arch/x86/kernel/devicetree.c

We know how DT based ioapics are added. No need to point to it.

> In case of IOAPIC_DOMAIN_DYNAMIC (DT/OF based system), 'ioapic_dynirq_base'
> remains to zero initialized value. This means that for OF based systems,
> virtual IRQ base will get set to zero. Zero value for a virtual IRQ is a
> invalid value.
> Please see https://yarchive.net/comp/linux/zero.html for more details.

First of all, please do not use random archive links. See
Documentation/process/ how links to LKML archives should look like

Secondly, this link is irrelevant. ioapic_dynirq_base has nothing to do
with virtual IRQ number 0. It's a boundary for the dynamic allocation of
virtual interrupt numbers so that the core allocator does not pick
interrupts out of the IOAPIC's fixed interrupt number space.

This can be legitimately 0 when IOAPIC is not enabled at all.

Can you please explain what kind of problem you were seing and what this
really fixes?

Thanks,

	tglx