[Bug 67813] [HSW bisected]igt/module_reload causes [drm:hsw_unclaimed_reg_check] *ERROR* Unclaimed write to 44004 and system hang with headless, with power well disabled

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=67813

--- Comment #39 from Paulo Zanoni <przanoni at gmail.com> ---
(In reply to comment #38)
> I did some more investigation, and it seems the Kernel gets stuck on an
> infinite loop that keeps calling VGA. I added some printks, and I at the
> moment we do the "echo 0" to the bind file

(accidentally hit the "Save Changes" button)

I did some more investigation, and it seems the Kernel gets stuck on an
infinite loop that keeps calling VGA functions. I added some printks, and at
the moment we do the "echo 0" to the bind file, we keep printing this forever:

[  431.878277] === write_vga
[  431.878278] === vgacon_set_cursor_size
[  431.878297] [drm:intel_uncore_check_errors] *ERROR* Unclaimed register
before interrupt
[  431.878331] === vgacon_cursor  
[  431.878332] === vgacon_restore_screen
[  431.878332] === write_vga  
[  431.878333] === vgacon_set_cursor_size  
[  431.878373] === vgacon_dummy
[  431.878373] === vgacon_scroll  
[  431.878374] === vgacon_restore_screen  
[  431.878374] === vgacon_scrollback_update  
[  431.878435] === vga_set_mem_top  
[  431.878435] === write_vga  
[  431.878439] === vgacon_dummy  
[  431.878440] === vgacon_scroll
[  431.878440] === vgacon_restore_screen  
[  431.878440] === vgacon_scrollback_update  
[  431.878501] === vga_set_mem_top  
[  431.878502] === write_vga  
[  431.878503] === vgacon_cursor  
[  431.878503] === vgacon_restore_screen  
[  431.878504] === write_vga  
[  431.878505] === vgacon_set_cursor_size  
[  431.878524] [drm:intel_uncore_check_errors] *ERROR* Unclaimed register
before interrupt
[  431.878559] === vgacon_cursor  
[  431.878559] === vgacon_restore_screen  
[  431.878559] === write_vga  
[  431.878560] === vgacon_set_cursor_size
[  431.878601] === vgacon_dummy  
[  431.878601] === vgacon_scroll 

Also, the function that triggers the unclaimed register is clearly
vgacon_set_cursor_size.

It looks like we're stuck in an infinite loop inside console_unlock.

The code that seems to fix the problem is just:
vga_get_uninterruptible(dev->pdev, VGA_RSRC_LEGACY_IO);
val = inb(VGA_MSR_READ);
outb(val & ~VGA_MSR_MEM_EN, VGA_MSR_WRITE);
vga_set_legacy_decoding(dev->pdev, VGA_RSRC_LEGACY_IO | VGA_RSRC_NORMAL_IO
|VGA_RSRC_NORMAL_MEM);
vga_put(dev->pdev, VGA_RSRC_LEGACY_IO);

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