Hi, I am working on adding AMD related drivers support for PCIe BARs 
move feature developed by Sergei 
(https://linuxplumbersconf.org/event/7/contributions/847/attachments/584/1035/lpc2020_sergmir.pdf).
His feature is still not upstream, all his code and mine on top can be 
seen here - 
https://cgit.freedesktop.org/~agrodzov/linux/log/?h=yadro/pcie_hotplug/movable_bars_v9.1
I did basic implementation fro amdgpu driver and now I am doing the same 
for snd_hda_intel to support our on GPU Azalia audio chips. This 
relevant commit is here - 
https://cgit.freedesktop.org/~agrodzov/linux/commit/?h=yadro/pcie_hotplug/movable_bars_v9.1&id=7ec0f60633e898cb941cebb3cd18aae1374fc365
Any driver that wants to support movable BARs needs to implement 
rescan_prepare, rescan_done and bar_fixed callbacks where rescan_prepare 
needs to stop HW/SW and unamp all MMIO mappings and rescan_done needs to 
ioremap the BAR from it's new MMIO location and restart HW/SW.

I am able currently to trigger BARs move by sysfs using 
"/sys/bus/pci/rescan" and the driver will go through the sequence I 
described above without hangs. Problem is that after this when i try to 
use mplayer I am getting following errors:

andrey@andrey-test:~$ sudo mplayer -ao alsa:device=hw=0.3 
Downloads/file_example_MP3_5MG.mp3
MPlayer 1.3.0 (Debian), built with gcc-9 (C) 2000-2016 MPlayer Team
do_connect: could not connect to socket
connect: No such file or directory
Failed to open LIRC support. You will not be able to use your remote 
control.

Playing Downloads/file_example_MP3_5MG.mp3.
libavformat version 58.29.100 (external)
Audio only file format detected.
Load subtitles in Downloads/
==========================================================================
Opening audio decoder: [mpg123] MPEG 1.0/2.0/2.5 layers I, II, III
AUDIO: 44100 Hz, 2 ch, s16le, 320.0 kbit/22.68% (ratio: 40000->176400)
Selected audio codec: [mpg123] afm: mpg123 (MPEG 1.0/2.0/2.5 layers I, 
II, III)
==========================================================================
AO: [alsa] 44100Hz 2ch s16le (2 bytes per sample)
Video: no video
Starting playback...
A:   0.1 (00.0) of 132.0 (02:12.0) ??,?%
Audio device got stuck!

and in dmesg I see
[  365.355518] snd_hda_codec_hdmi hdaudioC0D0: Unable to sync register 
0x2f0d00. -5

Also I see 296.619014] snd_hda_intel 0000:0a:00.1: CORB reset timeout#2, 
CORBRP = 65535 error during the rescan_done callback execution

I know it has to do with the move of BAR's MMIO address because when i
disallow BAR migration by returning true from bar_fixed callback I have 
no such errors and mplayer works fine.

I enabled MMIO trace and didn't see that post BAR move there is a wrong 
MMIO access - all of them are from the new MMIO base offset - 0xfcd80000 
(trace attached including mmio trace and dmesg)

I would be happy for any idea on this and any comment on the correctness 
of my sequence in the code

Andrey