Re: [PATCH 1/2] usb: typec: tcpm: improve handling of DISCOVER_MODES failures

[Badhri Jagan Sridharan]

On Fri, Feb 13, 2026 at 11:48 AM Sebastian Reichel
<sebastian.reichel@xxxxxxxxxxxxx> wrote:
>
> UGREEN USB-C Multifunction Adapter Model CM512 (AKA "Revodok 107")
> exposes two SVIDs: 0xff01 (DP Alt Mode) and 0x1d5c. The DISCOVER_MODES
> step succeeds for 0xff01 and gets a NAK for 0x1d5c. Currently this
> results in DP Alt Mode not being registered either, since the modes are
> only registered once all of them have been discovered. The NAK results
> in the processing being stopped and thus no Alt modes being registered.
>
> Improve the situation by handling the NAK gracefully and continue
> processing the other modes.
>
> Signed-off-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>

In v2, dont forget to add "Fixes:" and "Cc: stable@xxxxxxxxxxxxxxx"

Thanks,
Badhri

> ---
>  drivers/usb/typec/tcpm/tcpm.c | 40 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 39 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index be49a976428f..88cc27ad9514 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -2329,8 +2329,46 @@ static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
>                 switch (cmd) {
>                 case CMD_DISCOVER_IDENT:
>                 case CMD_DISCOVER_SVID:
> -               case CMD_DISCOVER_MODES:
>                 case VDO_CMD_VENDOR(0) ... VDO_CMD_VENDOR(15):
> +                       break;
> +               case CMD_DISCOVER_MODES:
> +                       tcpm_log(port, "Skip SVID 0x%04x (failed to discover mode)",
> +                                PD_VDO_SVID_SVID0(p[0]));
> +
> +                       if (rx_sop_type == TCPC_TX_SOP) {
> +                               /* 6.4.4.3.3 */
> +                               modep->svid_index++;
> +                               if (modep->svid_index < modep->nsvids) {
> +                                       u16 svid = modep->svids[modep->svid_index];
> +                                       *response_tx_sop_type = TCPC_TX_SOP;
> +                                       response[0] = VDO(svid, 1, svdm_version,
> +                                                         CMD_DISCOVER_MODES);
> +                                       rlen = 1;
> +                               } else if (tcpm_cable_vdm_supported(port)) {
> +                                       *response_tx_sop_type = TCPC_TX_SOP_PRIME;
> +                                       response[0] = VDO(USB_SID_PD, 1,
> +                                                         typec_get_cable_svdm_version(typec),
> +                                                         CMD_DISCOVER_SVID);
> +                                       rlen = 1;
> +                               } else {
> +                                       tcpm_register_partner_altmodes(port);
> +                               }
> +                       } else if (rx_sop_type == TCPC_TX_SOP_PRIME) {
> +                               /* 6.4.4.3.3 */
> +                               modep_prime->svid_index++;
> +                               if (modep_prime->svid_index < modep_prime->nsvids) {
> +                                       u16 svid = modep_prime->svids[modep_prime->svid_index];
> +                                       *response_tx_sop_type = TCPC_TX_SOP_PRIME;
> +                                       response[0] = VDO(svid, 1,
> +                                                         typec_get_cable_svdm_version(typec),
> +                                                         CMD_DISCOVER_MODES);
> +                                       rlen = 1;
> +                               } else {
> +                                       tcpm_register_plug_altmodes(port);
> +                                       tcpm_register_partner_altmodes(port);
> +                               }
> +                       }
> +
>                         break;
>                 case CMD_ENTER_MODE:
>                         /* Back to USB Operation */
>
> --
> 2.51.0
>