set-samsung-speed.sh

gistfile1.txt

#!/bin/bash
#
# script to set link speed of Samsung NVMe SSDs to $1
#
# almost completely based on https://www.alexforencich.com/wiki/en/pcie/set-speed
# (archived at https://archive.ph/dRb6z)

export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

setspeed() {
	dev=$1
	speed=$2

	if [ ! -e "/sys/bus/pci/devices/$dev" ]; then
		dev="0000:$dev"
	fi

	if [ ! -e "/sys/bus/pci/devices/$dev" ]; then
		echo "Error: device $dev not found"
		exit 1
	fi

	pciec=$(setpci -s $dev CAP_EXP+02.W)
	pt=$((("0x$pciec" & 0xF0) >> 4))

	port=$(basename $(dirname $(readlink "/sys/bus/pci/devices/$dev")))

	if (($pt == 0)) || (($pt == 1)) || (($pt == 5)); then
		dev=$port
	fi

	lc=$(setpci -s $dev CAP_EXP+0c.L)
	ls=$(setpci -s $dev CAP_EXP+12.W)

	max_speed=$(("0x$lc" & 0xF))

	echo "Link capabilities:" $lc
	echo "Max link speed:" $max_speed
	echo "Link status:" $ls
	echo "Current link speed:" $(("0x$ls" & 0xF))

	if [ -z "$speed" ]; then
		speed=$max_speed
	fi

	if (($speed > $max_speed)); then
		speed=$max_speed
	fi

	echo "Configuring $dev..."

	lc2=$(setpci -s $dev CAP_EXP+30.L)

	echo "Original link control 2:" $lc2
	echo "Original link target speed:" $(("0x$lc2" & 0xF))

	lc2n=$(printf "%08x" $((("0x$lc2" & 0xFFFFFFF0) | $speed)))

	echo "New target link speed:" $speed
	echo "New link control 2:" $lc2n

	setpci -s $dev CAP_EXP+30.L=$lc2n

	echo "Triggering link retraining..."

	lc=$(setpci -s $dev CAP_EXP+10.L)

	echo "Original link control:" $lc

	lcn=$(printf "%08x" $(("0x$lc" | 0x20)))

	echo "New link control:" $lcn

	setpci -s $dev CAP_EXP+10.L=$lcn

	sleep 0.1

	ls=$(setpci -s $dev CAP_EXP+12.W)

	echo "Link status:" $ls
	echo "Current link speed:" $(("0x$ls" & 0xF))
} # setspeed

LinkSpeed="$1"
if [ -z "${LinkSpeed}" ]; then
	echo "Error: no link speed specified. Needs to be 1 to 4. Exiting"
	exit 1
fi

lspci | awk -F" " '/Samsung/ {print $1}' | while read ; do
	setspeed "${REPLY}" ${LinkSpeed} >/dev/null
done