[PATCH] usb: typec: tbt: Correct swapped TBT adapter type values
From: Sven Peter
Date: Tue Aug 18 2026 - 12:20:54 EST
Table F-10 of the USB Type-C Cable and Connector Specification R2.5 on
page 412 defines bit 16 of the TBT3 Device Discover Mode VDO as 0 = TBT3
Adapter and 1 = TBT2 Legacy Adapter. Linux has those two swapped since
their original introduction in commit ca469c292edc ("usb: typec: Add
definitions for Thunderbolt 3 Alternate Mode").
ChromiumOS EC's include/usb_pd_tbt.h has them the correct way around
and references the USB Type-C ECN "Thunderbolt 3 Compatibility Updates"
as fixing an error where they were originally swapped which is presumably
where the wrong order originally came from.
I've also confirmed the correct mapping with an Apple Thunderbolt 3
to Thunderbolt 2 adapter which does set bit 16 in that VDO.
Swap the two values and update all users. Also rename the old defines
so that no user accidentally ends up with an inverted value.
No functional change.
Link: https://usb.org/document-library/usb-type-cr-cable-and-connector-specification-release-25
Link: https://chromium.googlesource.com/chromiumos/platform/ec/+/db93814b6e73c8545d23714fe0674c10814d901a/include/usb_pd_tbt.h#90
Signed-off-by: Sven Peter <sven@xxxxxxxxxx>
---
I ran into this when bringing up thunderbolt for Apple Silicon SoCs and
was very confused why the condition for "tbt2 adapter" vs "tbt3 adapter"
seemed to be backwards.
I think the qcom pmic_glink_altmode.c actually has a bug there that was
hidden and/or caused by the wrong values: It used to always set
TBT_ADAPTER_TBT3 which sounds plausible but actually claims to be a
legacy TBT2 adapter on the wire. I don't have the hardware or know the
intention there though.
The other users look correct to me since they just pass the value
through.
---
drivers/platform/chrome/cros_ec_typec.c | 2 +-
drivers/soc/qcom/pmic_glink_altmode.c | 2 +-
drivers/usb/typec/mux/intel_pmc_mux.c | 2 +-
include/linux/usb/typec_tbt.h | 4 ++--
4 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/platform/chrome/cros_ec_typec.c b/drivers/platform/chrome/cros_ec_typec.c
index c0806c562bb9..79968edc16ed 100644
--- a/drivers/platform/chrome/cros_ec_typec.c
+++ b/drivers/platform/chrome/cros_ec_typec.c
@@ -586,7 +586,7 @@ static int cros_typec_enable_tbt(struct cros_typec_data *typec,
data.device_mode = TBT_MODE;
if (pd_ctrl->control_flags & USB_PD_CTRL_TBT_LEGACY_ADAPTER)
- data.device_mode = TBT_SET_ADAPTER(TBT_ADAPTER_TBT3);
+ data.device_mode = TBT_SET_ADAPTER(TBT_ADAPTER_TYPE_TBT2_LEGACY);
/* Cable Discover Mode VDO */
data.cable_mode = TBT_MODE;
diff --git a/drivers/soc/qcom/pmic_glink_altmode.c b/drivers/soc/qcom/pmic_glink_altmode.c
index 619bad2c27ee..8d4f54c160c5 100644
--- a/drivers/soc/qcom/pmic_glink_altmode.c
+++ b/drivers/soc/qcom/pmic_glink_altmode.c
@@ -215,7 +215,7 @@ static void pmic_glink_altmode_enable_tbt(struct pmic_glink_altmode *altmode,
/* Device Discover Mode VDO */
tbt_data.device_mode = TBT_MODE;
- tbt_data.device_mode |= TBT_SET_ADAPTER(TBT_ADAPTER_TBT3);
+ tbt_data.device_mode |= TBT_SET_ADAPTER(TBT_ADAPTER_TYPE_TBT2_LEGACY);
/* Cable Discover Mode VDO */
tbt_data.cable_mode = TBT_MODE;
diff --git a/drivers/usb/typec/mux/intel_pmc_mux.c b/drivers/usb/typec/mux/intel_pmc_mux.c
index 219a32da1348..b63114575a78 100644
--- a/drivers/usb/typec/mux/intel_pmc_mux.c
+++ b/drivers/usb/typec/mux/intel_pmc_mux.c
@@ -346,7 +346,7 @@ pmc_usb_mux_tbt(struct pmc_usb_port *port, struct typec_mux_state *state)
req.mode_data = (port->orientation - 1) << PMC_USB_ALTMODE_ORI_SHIFT;
req.mode_data |= (port->role - 1) << PMC_USB_ALTMODE_UFP_SHIFT;
- if (TBT_ADAPTER(data->device_mode) == TBT_ADAPTER_TBT3)
+ if (TBT_ADAPTER(data->device_mode) == TBT_ADAPTER_TYPE_TBT2_LEGACY)
req.mode_data |= PMC_USB_ALTMODE_TBT_TYPE;
if (data->cable_mode & TBT_CABLE_OPTICAL)
diff --git a/include/linux/usb/typec_tbt.h b/include/linux/usb/typec_tbt.h
index 0b570f1b8bc8..7bdf3795ae50 100644
--- a/include/linux/usb/typec_tbt.h
+++ b/include/linux/usb/typec_tbt.h
@@ -27,8 +27,8 @@ struct typec_thunderbolt_data {
/* TBT3 Device Discover Mode VDO bits */
#define TBT_MODE BIT(0)
#define TBT_ADAPTER(_vdo_) FIELD_GET(BIT(16), _vdo_)
-#define TBT_ADAPTER_LEGACY 0
-#define TBT_ADAPTER_TBT3 1
+#define TBT_ADAPTER_TYPE_TBT3 0
+#define TBT_ADAPTER_TYPE_TBT2_LEGACY 1
#define TBT_INTEL_SPECIFIC_B0 BIT(26)
#define TBT_VENDOR_SPECIFIC_B0 BIT(30)
#define TBT_VENDOR_SPECIFIC_B1 BIT(31)
---
base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
change-id: 20260818-b4-tbt-legacy-fix-d6e71ac4bb6a
Best regards,
--
Sven Peter <sven@xxxxxxxxxx>