linux-kernel - Re: [PATCH] x86/i8259: Work around buggy legacy PIC

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Message-ID: <87im3l43w9.ffs@nanos.tec.linutronix.de>
Date:   Fri, 14 May 2021 19:32:54 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Maximilian Luz <luzmaximilian@...il.com>,
        Sachi King <nakato@...ato.io>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        David Laight <David.Laight@...lab.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        "x86\@kernel.org" <x86@...nel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable\@vger.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] x86/i8259: Work around buggy legacy PIC

On Fri, May 14 2021 at 13:58, Maximilian Luz wrote:
> On 5/14/21 9:41 PM, Sachi King wrote:
> I'd assume that _some_ sort of interrupt setup is done by the BIOS/UEFI.
> The UEFI on those devices is fairly well-featured, with touch support
> via SPI and all. Furthermore, keyboard (also supported in the device's
> UEFI) is handled via a custom UART protocol. Unless they rely on polling
> for all of that, I believe they'd have to set up some interrupts.

Polling would be truly surprising.

> Although, as you mention later on, that could also be handled via the
> IOAPIC and the PIC is actually not supposed to be used. Maybe some
> legacy component that never got tested and just broke with some new
> hardware/firmware revision without anyone noticing? And since Linux
> still seems to rely on that, we might be the first to notice.

That's a valid assumption. As I said, we can make IOAPIC work even w/o
PIC. I'll have a look how much PIC assumptions are still around.

Thanks,

        tglx