kernel error: Bluetooth: hci0: No support for _PRR ACPI methodThe kernel: Bluetooth: hci0: No support for _PRR ACPI method

This message is a non-critical, warning indicating that your system's ACPI (firmware) doesn't have a defined method for a hardware-level Bluetooth radio reset. This is typically a minor firmware-level issue that does not affect Bluetooth functionality but may appear in your system's boot logs. Here is a breakdown of what the message means and potential solutions:

What the message means:

• ACPI: Advanced Configuration and Power Interface. It is a standard that allows the operating system to manage the power, thermal, and configuration aspects of the hardware.
• hci0: The host controller interface for the first Bluetooth adapter.
• _PRR: This is an ACPI "control method" object, which stands for "Power Resource for Reset". It provides a standardized way for the operating system to perform a hardware-level reset of a device, such as a Bluetooth radio.
• "No support for _PRR ACPI method": The message means that the Linux kernel tried to find and use this standard reset method for your Bluetooth controller but could not find the corresponding instruction in your system's ACPI firmware. 

Potential fixes:

1. Ignore the warning. In most cases, the warning is harmless. If your Bluetooth is working correctly, you don't need to do anything. You can suppress the message from appearing in your boot logs by following the steps in the next section. 
2. Suppress the message in the boot log. You can hide this specific message from your boot log by changing the kernel's log level. This is a purely cosmetic fix.
   1. Locate the line that begins with GRUB_CMDLINE_LINUX_DEFAULT.
   2. Change the line from GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" to GRUB_CMDLINE_LINUX_DEFAULT="quiet splash loglevel=3".
   3. Save the changes and exit the editor.
   4. Reboot your system to apply the changes. 
   5. Update GRUB with the following command:

sudo update-grub

Open the GRUB configuration file by running

sudo vim /etc/default/grub

3. Update your system's BIOS. An outdated BIOS can be the cause of this and other ACPI-related errors. Manufacturers may release BIOS updates that add or correct ACPI methods for hardware components.
   1. Check your computer manufacturer's website for the latest BIOS/firmware update for your specific model.
   2. Refer to your manufacturer's instructions for the correct update procedure. 
4. Update the Linux kernel. For some users, upgrading or downgrading the Linux kernel has resolved Bluetooth or ACPI-related issues. Some Linux distributions may have introduced a bug in a newer kernel version that can be fixed by downgrading. Conversely, a new kernel may contain fixes for ACPI issues. 
5. Report the bug to coreboot (for compatible devices). If you are using coreboot, an open-source alternative to proprietary BIOS/UEFI firmware, you may find a fix has been added or is being developed. For instance, a patch for this specific issue on Intel Bluetooth was posted to the coreboot Gerrit. 

When to worry:

You should investigate the issue further if you experience any of the following problems:

• Your Bluetooth hardware is not detected.
• You are unable to connect to Bluetooth devices.
• Your Bluetooth connection is unstable or drops frequently. 

If you encounter these issues, the log message may point to an underlying problem with your Bluetooth device or system firmware.