linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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)


  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=bbf5d417ee0d4edbbed31f19ef40fad0@AcuMS.aculab.com \
    --to=david.laight@aculab.com \
    --cc=bp@alien8.de \
    --cc=hpa@zytor.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luzmaximilian@gmail.com \
    --cc=mingo@redhat.com \
    --cc=nakato@nakato.io \
    --cc=stable@vger.kernel.org \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).