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From: Thomas Gleixner <tglx@linutronix.de>
To: "Kirkendall, Garrett" <Garrett.Kirkendall@amd.com>
Cc: "nstange@suse.de" <nstange@suse.de>,
	"luto@kernel.org" <luto@kernel.org>,
	"natechancellor@gmail.com" <natechancellor@gmail.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: arch/x86/kernel/apic/apic.c: calibrate_APIC_clock() soft hangs when PIC is not configured by BIOS before kernel is launched.
Date: Fri, 14 Jun 2019 15:02:43 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1906141454430.1722@nanos.tec.linutronix.de> (raw)
In-Reply-To: <SN6PR12MB2734370504CF4B89600C8FD885330@SN6PR12MB2734.namprd12.prod.outlook.com>

Garrett,

On Thu, 9 May 2019, Kirkendall, Garrett wrote:

  A: Because it messes up the order in which people normally read text.
  Q: Why is top-posting such a bad thing?
  A: Top-posting.
  Q: What is the most annoying thing in e-mail?

  A: No.
  Q: Should I include quotations after my reply?

  http://daringfireball.net/2007/07/on_top

Also please break the lines around 78 chars.

> 1.  Is it correct to probe the 8259 before it is initialized by the
>     kernel?  The 8259 will not respond properly to the probe unless it is
>     properly initialized.

So far the kernel relied on the BIOS to initialize 8259

> 2.  Should IOAPIC interrupts 0-15 require the legacy PIC be available and
>     initialized by the BIOS?

Unless the platform explicitely states that there is no legacy PIC, which
is true for some MID and HV guest systems. 

> 2.  The kernel will not boot if there is no legacy 8259 PIC even if all
>     the other factors stated are provided.

Hmm? what other factors?

> I want to understand why a preinitialized 8259 is a requirement for a
> system configured to use the IOAPIC?

Mostly historical reasons and the whole PIC/IOAPIC thing has been a fragile
nightmare forever, so I'm reluctant to do any extra work there which might
break older machines.

Thanks,

	tglx

      reply	other threads:[~2019-06-14 13:02 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <SN6PR12MB2734813FB27C43E06F5B4E3D85330@SN6PR12MB2734.namprd12.prod.outlook.com>
2019-05-09 13:24 ` arch/x86/kernel/apic/apic.c: calibrate_APIC_clock() soft hangs when PIC is not configured by BIOS before kernel is launched Kirkendall, Garrett
2019-05-09 13:32   ` Thomas Gleixner
2019-05-09 14:15     ` Kirkendall, Garrett
2019-06-14 13:02       ` Thomas Gleixner [this message]

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