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+====== PCIe Set Speed ======
+This script uses setpci to change a device's target link speed.  This can be useful when using a PCIe protocol analyzer that does not support PCIe gen 3.  It can also be helpful for testing a device at a lower bandwidth.
+<code sh>
+#!/bin/bash
+dev=$1
+speed=$2
+if [ -z "$dev" ]; then
+    echo "Error: no device specified"
+    exit 1
+fi
+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))
+</code>

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