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Date:   Sun, 30 Jan 2022 14:10:20 +0300
From:   Alexander Sergeyev <sergeev917@gmail.com>
To:     Takashi Iwai <tiwai@suse.de>
Cc:     Jeremy Szu <jeremy.szu@canonical.com>, tiwai@suse.com,
        "moderated list:SOUND" <alsa-devel@alsa-project.org>,
        Kailang Yang <kailang@realtek.com>,
        open list <linux-kernel@vger.kernel.org>,
        Huacai Chen <chenhuacai@kernel.org>,
        Jian-Hong Pan <jhp@endlessos.org>,
        Hui Wang <hui.wang@canonical.com>,
        PeiSen Hou <pshou@realtek.com>
Subject: Re: [PATCH 1/4] ALSA: hda/realtek: fix mute/micmute LEDs for HP 855
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On Sat, Jan 29, 2022 at 05:47:07PM +0300, Alexander Sergeyev wrote:
> But unbind-bind problems with IO_PAGE_FAULT and "out of range cmd" are not 
> eliminated. IO_PAGE_FAULT are often logged without accompanying "out of range 
> cmd". And after adding debugging printk() I haven't managed to trigger "out 
> of range cmd" yet. But IO_PAGE_FAULT are more easily triggered.

IO_PAGE_FAULTs go away with CONFIG_IOMMU_DEFAULT_PASSTHROUGH enabled. As I 
understand, this leads to reduced DMA device isolation which is generally not 
desirable. I was initially thinking about races between some delayed code and 
io-memory pages unmapping, but first IO_PAGE_FAULTs (running non-passthrough 
iommu) happen during bind operations as well.

What is also interesting, unbind & bind consistently fails on 31th bind:

echo -n '0000:05:00.6' > /sys/bus/pci/drivers/snd_hda_intel/bind
-bash: echo: write error: No such device

And does not recover from there until a reboot.