Re: [PATCH 1/1] nfc: nci: ignore unexpected CORE_RESET_NTF

[Yuchao Zhang <ndaugoing@gmail.com>]

Hi Simon,

Thank you (and the sashiko reviewer) for the thorough review.
The points raised are completely valid and insightful.

1. Regarding FDP firmware update breakage (Severity: High):
You are absolutely right. In nci_ntf_packet(), returning -EINVAL from
nci_core_reset_ntf_packet() aborts the dispatch pipeline (goto end), which
prevents nci_core_ntf_packet() from running driver-specific handlers. In
drivers/nfc/fdp/fdp.c, the firmware patching path relies on this spontaneous
CORE_RESET_NTF to wake up info->setup_wq; dropping the packet causes it to
block indefinitely.

As suggested, in v2 we drop only the core-level bookkeeping (skipping the
ndev->nci_ver update and nci_req_complete) and return 0 so that driver-registered
ops continue to receive the notification.

2. Regarding ntf->reset_trigger (Severity: Medium):
The reset_trigger field is revision-dependent: in NCI 1.0, CORE_RESET_CMD
is reported as 0x00 (0x01 is powered-on), while NCI 2.0 defines 0x00 as
an unrecoverable error and reports CORE_RESET_CMD as 0x02. Hardcoding
either value would break the other generation of devices, so v2 gates
the core bookkeeping on NCI_RESET_PENDING alone and only skips power-on
notifications (trigger 0x01, which means the same in both revisions).
Power-on notifications never overlap a pending reset in the protocol
flow, and both revision's command-triggered values reach the flag gate.

3. Regarding nci_core_reset_rsp_packet() (Severity: Medium):
Agreed. nci_core_reset_rsp_packet() now checks whether NCI_RESET_PENDING
is set before calling nci_req_complete() on non-OK or NCI 1.x responses to avoid
prematurely completing an unrelated request.

4. Regarding NCI 1.x response length check (Severity: Low):
In v2, we explicitly check skb->len >= sizeof(*rsp) to ensure config_status is
not read out-of-bounds in pr_debug().

5. Regarding request serialization / stale notifications (Severity: Medium):
All requests are serialized under ndev->req_lock, and __nci_request() unconditionally
clears NCI_RESET_PENDING before dropping req_lock. Filtering out power-on notifications
(trigger 0x01) ensures spontaneous controller power-ups are ignored, while checking and
clearing the pending flag ensures each command matches at most one notification.

6. Regarding request generation (Severity: Medium on both questions):
The NCI protocol gives notifications no request correlation, so a stale
CORE_RESET_NTF/RSP that is already inside nci_rx_work when a reset times
out and userspace retries cannot be distinguished from the new attempt's
own frame: the flag gate and the trigger check narrow the window, but a
generation identity would require protocol support that does not exist.
The failure path purges queued frames; only an in-flight worker frame can
straddle, and the data it carries originates from the same controller.
If you would prefer, I can add a per-request generation check for the RSP
path where an identity exists, as a follow-up.

v2 patch has been sent as reply to this thread.

Thanks,
Yuchao