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From:   tedheadster <tedheadster@gmail.com>
Date:   Thu, 7 Feb 2019 08:00:14 -0500
Message-ID: <CAP8WD_YG_qirbSoVtyYoWRhZeON6p2RbN06B_yGQk1pA3==UTg@mail.gmail.com>
Subject: [4.17 Regression]: x86/dma: Use DMA-direct
To:     Christoph Hellwig <hch@infradead.org>,
        Fenghua Yu <fenghua.yu@intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Christoph,
  in the 4.17 cycle you submitted the patch "x86/dma: Use DMA-direct".
This causes the VGA video on my laptop to stop working, but the system
continues to be up and functioning. Video works until about 3/4 the
way through boot, when I think it is loading a video driver, and then
video hangs. I could ssh to it and the keyboard would respond to
alt-sysrq commands.

Strangely, it started working again in the 4.20 cycle with the
addition of Fenghua's patch "x86/cpufeatures: Enumerate MOVDIRI
instruction". This is odd to me because it looks like a very simple
patch.

I only have CONFIG_VGA_CONSOLE, CONFIG_FRAMEBUFFER_CONSOLE and
CONFIG_FRAMEBUFFER_CONSOLE_DETECT_PRIMARY enabled, with no
hardware-specific framebuffer config option set.

lspci -nn of my VGA adapter gives the following:

00:02.0 VGA compatible controller [0300]: Intel Corporation
82852/855GM Integrated Graphics Device [8086:3582] (rev 02)

Your thoughts? How can I help debug this?

Reported-by: Matthew Whitehead <tedheadster@gmail.com>