thunderbolt: Do not allow subtracting more NFC credits than configured

This might happen if the boot firmware uses different amount of NFC
credits than what the router suggests, or we are dealing with pre-USB4
device.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
index 3014146081c19f61c121fd321f807b166d6ca77e..463cfdc0b42f5f4a3f6d2f7a0344e000d1cf5419 100644 (file)
--- a/drivers/thunderbolt/switch.c
+++ b/drivers/thunderbolt/switch.c
@@ -623,6 +623,9 @@ int tb_port_add_nfc_credits(struct tb_port *port, int credits)
                return 0;
 
        nfc_credits = port->config.nfc_credits & ADP_CS_4_NFC_BUFFERS_MASK;
+       if (credits < 0)
+               credits = max_t(int, -nfc_credits, credits);
+
        nfc_credits += credits;
 
        tb_port_dbg(port, "adding %d NFC credits to %lu", credits,