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Document acpi_rev_override kernel parameter #174

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Document acpi_rev_override kernel parameter #174

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28 changes: 19 additions & 9 deletions README.md
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Expand Up @@ -22,15 +22,25 @@ detect the correct handle preceding _DSM and has some built-in safeguards:
disabled again if that was the case before suspending. Hibernation should
work, but it not tested.

Precautionary measure :
- On some machines, turning off the card is permanent and the card does not
reappear on subsequents reboots, which can result into the screen staying
black all the time, including the BIOS screen.
If it occurs, first try to shutdown, unplug power cord, remove battery, wait
30s, then put everything back in and boot. If it's not solved, then the
solution is to reset the BIOS to factory settings. Before executing bbswitch
for the first time, it is therefore recommended to take note of the full key
sequence in the BIOS to do a reset.
Preparation
-----------

### Precautionary measure

On some machines, turning off the card is permanent and the card does not
reappear on subsequents reboots, which can result into the screen staying
black all the time, including the BIOS screen.
If it occurs, first try to shutdown, unplug power cord, remove battery, wait
30s, then put everything back in and boot. If it's not solved, then the
solution is to reset the BIOS to factory settings. Before executing bbswitch
for the first time, it is therefore recommended to **take note of the full key
sequence in the BIOS to do a reset**.

### acpi_rev_override

On some computers (such as the Dell XPS 15 9560, [issue](https://github.com/Bumblebee-Project/bbswitch/issues/148)), you may have to set the `acpi_rev_override` parameter to `1` (`acpi_rev_override=1`). The absence of this parameter may cause a black screen at system boot.

See [this article](https://wiki.archlinux.org/index.php/Kernel_parameters) for setting and persisting kernel parameters.

Build
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