[PATCH 1/2] thunderbolt: Read DROM directly from NVM before trying bit banging

[Mario Limonciello]

Some TBT3 devices have a hard time reliably responding to bit banging
requests correctly when connected to AMD USB4 hosts running Linux.

These problems are not reported in any other CM, and comparing the
implementations the Linux CM is the only one that utilizes bit banging
to access the DROM. Other CM implementations access the DROM directly
from the NVM instead of bit banging.

Adjust the flow to try this on TBT3 devices before resorting to bit
banging.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
 drivers/thunderbolt/eeprom.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/thunderbolt/eeprom.c b/drivers/thunderbolt/eeprom.c
index c90d22f56d4e1..d9d9567bb938b 100644
--- a/drivers/thunderbolt/eeprom.c
+++ b/drivers/thunderbolt/eeprom.c
@@ -640,6 +640,10 @@ int tb_drom_read(struct tb_switch *sw)
 		return 0;
 	}
 
+	/* TBT3 devices have the DROM as part of NVM */
+	if (tb_drom_copy_nvm(sw, &size) == 0)
+		goto parse;
+
 	res = tb_drom_read_n(sw, 14, (u8 *) &size, 2);
 	if (res)
 		return res;
-- 
2.25.1