{bp-19371} drivers/usbdev: re-assert soft connect in cdcecm/cdcncm disconnect() - #19670
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The USB device controller drivers invoke CLASS_DISCONNECT() on every USB bus reset, and a bus reset is the first step of normal host enumeration. Every other class driver (cdcacm, usbmsc, rndis) re-asserts DEV_CONNECT() at the end of its disconnect() handler so that the device remains attached; cdcecm and cdcncm did not, so on controllers that soft-disconnect around bus reset (e.g. rp2040, which drops the pull-up in its bus-reset handler) a standalone CDC-ECM or CDC-NCM device is left soft-disconnected by the first bus reset and never enumerates on the host. Mirror the cdcacm behavior and perform the soft connect in the disconnect() methods, unless part of a composite device (composite.c already re-connects in its own disconnect handler). Fixes the standalone CDC-ECM case of issue apache#15880. Validated on raspberrypi-pico (RP2040): with this change a standalone CONFIG_NET_CDCECM device that previously never appeared on the host enumerates via cdc_ether and pings with 0% loss. cdcncm has the identical defect and receives the identical fix. Signed-off-by: Ricard Rosson <ricard@groundbits.com> Co-authored-by: Xiang Xiao <xiaoxiang781216@gmail.com> Assisted-by: Claude (Anthropic Claude Code)
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xiaoxiang781216
August 3, 2026 12:59
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Aug 3, 2026
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Summary
The USB device controller drivers invoke CLASS_DISCONNECT() on every USB bus reset, and a bus reset is the first step of normal host enumeration. Every other class driver (cdcacm, usbmsc, rndis) re-asserts DEV_CONNECT() at the end of its disconnect() handler so that the device remains attached; cdcecm and cdcncm did not, so on controllers that soft-disconnect around bus reset (e.g. rp2040, which drops the pull-up in its bus-reset handler) a standalone CDC-ECM or CDC-NCM device is left soft-disconnected by the first bus reset and never enumerates on the host.
Mirror the cdcacm behavior and perform the soft connect in the disconnect() methods, unless part of a composite device (composite.c already re-connects in its own disconnect handler).
Fixes the standalone CDC-ECM case of issue #15880.
Validated on raspberrypi-pico (RP2040): with this change a standalone CONFIG_NET_CDCECM device that previously never appeared on the host enumerates via cdc_ether and pings with 0% loss. cdcncm has the identical defect and receives the identical fix.
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