Hi,
On 11/13/22 19:59, Maximilian Luz wrote:
> Currently, we check any received packet whether we have already seen it
> previously, regardless of the packet type (sequenced / unsequenced). We
> do this by checking the sequence number. This assumes that sequence
> numbers are valid for both sequenced and unsequenced packets. However,
> this assumption appears to be incorrect.
>
> On some devices, the sequence number field of unsequenced packets (in
> particular HID input events on the Surface Pro 9) is always zero. As a
> result, the current retransmission check kicks in and discards all but
> the first unsequenced packet, breaking (among other things) keyboard and
> touchpad input.
>
> Note that we have, so far, only seen packets being retransmitted in
> sequenced communication. In particular, this happens when there is an
> ACK timeout, causing the EC (or us) to re-send the packet waiting for an
> ACK. Arguably, retransmission / duplication of unsequenced packets
> should not be an issue as there is no logical condition (such as an ACK
> timeout) to determine when a packet should be sent again.
>
> Therefore, remove the retransmission check for unsequenced packets
> entirely to resolve the issue.
>
> Fixes: c167b9c7e3d6 ("platform/surface: Add Surface Aggregator subsystem")
> Signed-off-by: Maximilian Luz <luzmaximilian@xxxxxxxxx>
Thank you for your patch-series, I've applied this series to my
fixes branch:
https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git/log/?h=fixes
Note it will show up in my fixes branch once I've pushed my
local branch there, which might take a while.
I will include this series in my next fixes pull-req to Linus
for the current kernel development cycle.
Regards,
Hans
> ---
> .../surface/aggregator/ssh_packet_layer.c | 24 +++++++++++++++----
> 1 file changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/platform/surface/aggregator/ssh_packet_layer.c b/drivers/platform/surface/aggregator/ssh_packet_layer.c
> index 6748fe4ac5d5..def8d7ac541f 100644
> --- a/drivers/platform/surface/aggregator/ssh_packet_layer.c
> +++ b/drivers/platform/surface/aggregator/ssh_packet_layer.c
> @@ -1596,16 +1596,32 @@ static void ssh_ptl_timeout_reap(struct work_struct *work)
> ssh_ptl_tx_wakeup_packet(ptl);
> }
>
> -static bool ssh_ptl_rx_retransmit_check(struct ssh_ptl *ptl, u8 seq)
> +static bool ssh_ptl_rx_retransmit_check(struct ssh_ptl *ptl, const struct ssh_frame *frame)
> {
> int i;
>
> + /*
> + * Ignore unsequenced packets. On some devices (notably Surface Pro 9),
> + * unsequenced events will always be sent with SEQ=0x00. Attempting to
> + * detect retransmission would thus just block all events.
> + *
> + * While sequence numbers would also allow detection of retransmitted
> + * packets in unsequenced communication, they have only ever been used
> + * to cover edge-cases in sequenced transmission. In particular, the
> + * only instance of packets being retransmitted (that we are aware of)
> + * is due to an ACK timeout. As this does not happen in unsequenced
> + * communication, skip the retransmission check for those packets
> + * entirely.
> + */
> + if (frame->type == SSH_FRAME_TYPE_DATA_NSQ)
> + return false;
> +
> /*
> * Check if SEQ has been seen recently (i.e. packet was
> * re-transmitted and we should ignore it).
> */
> for (i = 0; i < ARRAY_SIZE(ptl->rx.blocked.seqs); i++) {
> - if (likely(ptl->rx.blocked.seqs[i] != seq))
> + if (likely(ptl->rx.blocked.seqs[i] != frame->seq))
> continue;
>
> ptl_dbg(ptl, "ptl: ignoring repeated data packet\n");
> @@ -1613,7 +1629,7 @@ static bool ssh_ptl_rx_retransmit_check(struct ssh_ptl *ptl, u8 seq)
> }
>
> /* Update list of blocked sequence IDs. */
> - ptl->rx.blocked.seqs[ptl->rx.blocked.offset] = seq;
> + ptl->rx.blocked.seqs[ptl->rx.blocked.offset] = frame->seq;
> ptl->rx.blocked.offset = (ptl->rx.blocked.offset + 1)
> % ARRAY_SIZE(ptl->rx.blocked.seqs);
>
> @@ -1624,7 +1640,7 @@ static void ssh_ptl_rx_dataframe(struct ssh_ptl *ptl,
> const struct ssh_frame *frame,
> const struct ssam_span *payload)
> {
> - if (ssh_ptl_rx_retransmit_check(ptl, frame->seq))
> + if (ssh_ptl_rx_retransmit_check(ptl, frame))
> return;
>
> ptl->ops.data_received(ptl, payload);
