From: David Laight <David.Laight@ACULAB.COM>
To: 'Thomas Gleixner' <tglx@linutronix.de>,
'Maximilian Luz' <luzmaximilian@gmail.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Sachi King <nakato@nakato.io>,
"x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH] x86/i8259: Work around buggy legacy PIC
Date: Fri, 14 May 2021 13:13:19 +0000 [thread overview]
Message-ID: <bbf5d417ee0d4edbbed31f19ef40fad0@AcuMS.aculab.com> (raw)
In-Reply-To: <87tun54gg3.ffs@nanos.tec.linutronix.de>
From: Thomas Gleixner
> Sent: 14 May 2021 14:02
>
> David,
>
> On Thu, May 13 2021 at 10:36, David Laight wrote:
>
> >> -----Original Message-----
> >> From: Maximilian Luz <luzmaximilian@gmail.com>
>
> can you please fix your mail client and spare us the useless header
> duplication in the reply?
I have to delete them by hand - must have forgotten, I can't fix outlook :-)
> > It is also worth noting that the probe code is spectacularly crap.
> > It writes 0xff and then checks that 0xff is read back.
> > Almost anything (including a failed PCIe read to the ISA bridge)
> > will return 0xff and make the test pass.
>
> unsigned char probe_val = ~(1 << PIC_CASCADE_IR);
>
> outb(probe_val, PIC_MASTER_IMR);
> new_val = inb(PIC_MASTER_IMR);
>
> How is that writing 0xFF?
Sorry I misread the code and diagnostic output.
In any case writing a value and expecting the same value back
isn't exactly a high-quality probe.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-05-14 13:13 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 21:04 [PATCH] x86/i8259: Work around buggy legacy PIC Maximilian Luz
2021-05-13 8:10 ` David Laight
2021-05-13 10:11 ` Maximilian Luz
2021-05-13 10:36 ` David Laight
2021-05-14 13:01 ` Thomas Gleixner
2021-05-14 13:13 ` David Laight [this message]
2021-05-14 16:19 ` Ingo Molnar
2021-05-14 19:41 ` Sachi King
2021-05-14 10:51 ` David Laight
2021-05-14 11:58 ` Maximilian Luz
2021-05-14 17:32 ` Thomas Gleixner
2021-05-14 17:35 ` H. Peter Anvin
2021-05-14 22:47 ` Maximilian Luz
2021-05-17 18:40 ` Thomas Gleixner
2021-05-17 19:25 ` Maximilian Luz
2021-05-17 23:27 ` Thomas Gleixner
2021-05-18 8:28 ` Andy Shevchenko
2021-05-18 19:58 ` Sachi King
2021-05-18 15:45 ` Thomas Gleixner
2021-05-14 13:44 ` Thomas Gleixner
2021-05-14 16:12 ` David Laight
2021-05-14 17:28 ` H. Peter Anvin
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