Re: [PATCH] usb: typec: tbt: Correct swapped TBT adapter type values

On Tue, Aug 18, 2026 at 06:20:03PM +0200, Sven Peter wrote:
> 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 <[email protected]>

Shouldn't this be marked as a fix?

Reviewed-by: Heikki Krogerus <[email protected]>

> ---
> 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 <[email protected]>
> 

-- 
heikki