linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Maximilian Luz <luzmaximilian@gmail.com>
To: Sachi King <nakato@nakato.io>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	David Laight <David.Laight@aculab.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
	"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 13:58:49 +0200	[thread overview]
Message-ID: <5c08541a-2615-f075-a189-0462f1005007@gmail.com> (raw)
In-Reply-To: <3034083.sOBWI1P7ec@yuki>

On 5/14/21 9:41 PM, Sachi King wrote:
> On Thursday, May 13, 2021 8:36:27 PM AEST David Laight wrote:
>>> -----Original Message-----
>>> From: Maximilian Luz <luzmaximilian@gmail.com>
>>> Sent: 13 May 2021 11:12
>>> To: David Laight <David.Laight@ACULAB.COM>; Thomas Gleixner
>>> <tglx@linutronix.de>; 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; linux-kernel@vger.kernel.org; stable@vger.kernel.org
>>> Subject: Re: [PATCH] x86/i8259: Work around buggy legacy PIC
>>>
>>> On 5/13/21 10:10 AM, David Laight wrote:
>>>
>>>> From: Maximilian Luz
>>>>
>>>>> Sent: 12 May 2021 22:05
>>>>>
>>>>>
>>>>>
>>>>> The legacy PIC on the AMD variant of the Microsoft Surface Laptop 4
>>>>> has
>>>>> some problems on boot. For some reason it consistently does not
>>>>> respond
>>>>> on the first try, requiring a couple more tries before it finally
>>>>> responds.
>>>>
>>>>
>>>>
>>>> That seems very strange, something else must be going on that causes the
>>>> grief.
>>>> The 8259 will be built into to the one of the cpu support
>>>> chips.
>>>> I can't imagine that requires anything special.
>>>
>>>
>>> Right, it's definitely strange. Both Sachi (I imagine) and I don't know
>>> much about these devices, so we're open for suggestions.
>>
>>
>> I found a copy of the datasheet (I don't seem to have the black book):
>>
>> https://pdos.csail.mit.edu/6.828/2010/readings/hardware/8259A.pdf
>>
>> The PC hardware has two 8259 in cascade mode.
>> (Cascaded using an interrupt that wasn't really using in the original
>> 8088 PC which only had one 8259.)
>>
>> I wonder if the bios has actually initialised is properly.
>> Some initialisation writes have to be done to set everything up.
> 
> I suspect by the displayed behaviour you are correct and that it has
> not.  I'm struggling to figure out who to talk to to see that is
> something that can be fixed in the firmware.

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.

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.

Regards,
Max

  parent reply	other threads:[~2021-05-14 11:58 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
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 [this message]
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=5c08541a-2615-f075-a189-0462f1005007@gmail.com \
    --to=luzmaximilian@gmail.com \
    --cc=David.Laight@aculab.com \
    --cc=bp@alien8.de \
    --cc=hpa@zytor.com \
    --cc=linux-kernel@vger.kernel.org \
    --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).