[PATCH 07/19] thunderbolt: Don't read the UID if we already know it

On Apple Silicon the host router's UID comes from the DROM provided by
the device tree and is already known by the time tb_switch_set_uuid()
runs. Skip reading it from the config space again in that case.

For other USB4 hosts this only drops a duplicate read because
tb_drom_host_read() has already filled in the UID from ROUTER_CS_7
before tb_switch_set_uuid() runs. Device routers keep reading it
unconditionally.

Signed-off-by: Sven Peter <sven@kernel.org>
---
 drivers/thunderbolt/switch.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
index 404c0693df50..3f54a5ae56b0 100644
--- a/drivers/thunderbolt/switch.c
+++ b/drivers/thunderbolt/switch.c

@@ -2692,9 +2692,11 @@ static int tb_switch_set_uuid(struct tb_switch *sw)
 		return 0;
 
 	if (tb_switch_is_usb4(sw)) {
-		ret = usb4_switch_read_uid(sw, &sw->uid);
-		if (ret)
-			return ret;
+		if (tb_route(sw) || !sw->uid) {
+			ret = usb4_switch_read_uid(sw, &sw->uid);
+			if (ret)
+				return ret;
+		}
 		uid = true;
 	} else {
 		/*

-- 
2.55.0