Re: [PATCH net-next v2] net: wwan: mhi_wwan_ctrl: say the DTR drop flush is best effort

[Loic Poulain]

On Thu, Nov 12, 2026 at 6:22 PM Peter Hunt <peter.hunt@xxxxxxxxxxxx> wrote:
>
> Four comments around the DTR/RTS work don't match the code since
> commit 10f51f4fb99d ("net: wwan: mhi_wwan_ctrl: send a DTR drop before
> it can be coalesced"):
>
> - the ->dtr_rts() comment says the drop is sent now, but a drop that
>   hits a full UL ring or a failed allocation is retried with whatever
>   state is latest by then,
> - the stop() comment says pending state is sent before the channel
>   stops, but the flush there makes one attempt as well, and a retry
>   goes out from dtr_work after the channel has stopped,
> - the dtr_mdmbits comment only describes coalescing,
> - the remove() comment says the removal drop gets one attempt, but the
>   drop and stop() paths now flush the work as well.
>
> Update them. No functional change.
>
> Link: https://lore.kernel.org/all/179340002701.3131.15535297427661129303@xxxxxxxxxx/
> Signed-off-by: Peter Hunt <peter.hunt@xxxxxxxxxxxx>

Reviewed-by: Loic Poulain <loic.poulain@xxxxxxxxxxxxxxxx>

> ---
> Changes in v2:
> - Also update the stop() comment, its flush makes one attempt too.
> - Name a failed allocation as well as a full UL ring as a retry cause.
> - v1: https://lore.kernel.org/all/20261109185731.182990-1-peter.hunt@xxxxxxxxxxxx/
>
>  drivers/net/wwan/mhi_wwan_ctrl.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/wwan/mhi_wwan_ctrl.c b/drivers/net/wwan/mhi_wwan_ctrl.c
> index 772319927867..387ab1bb0c41 100644
> --- a/drivers/net/wwan/mhi_wwan_ctrl.c
> +++ b/drivers/net/wwan/mhi_wwan_ctrl.c
> @@ -68,7 +68,8 @@ struct mhi_wwan_dev {
>         unsigned int rx_budget;
>
>         /* Latest DTR/RTS state for the modem, sent from dtr_work so a burst of
> -        * changes is coalesced and only the final state has to get through
> +        * changes is coalesced and only the final state has to get through.
> +        * A DTR drop is flushed out on its own, see mhi_wwan_ctrl_dtr_rts().
>          */
>         unsigned int dtr_mdmbits;
>         struct delayed_work dtr_work;
> @@ -216,7 +217,9 @@ static void mhi_wwan_ctrl_dtr_rts(struct wwan_port *port, unsigned int mdmbits)
>         schedule_delayed_work(&mhiwwan->dtr_work, 0);
>
>         /* A DTR drop matters on its own, e.g. to hang up a modem set to AT&D2,
> -        * so send it now rather than let a following raise coalesce it away
> +        * so try to send it now rather than let a following raise coalesce it
> +        * away. This is best effort, a drop that hits a full UL ring or a failed
> +        * allocation is retried with whatever state is latest by then.
>          */
>         if (drop)
>                 flush_delayed_work(&mhiwwan->dtr_work);
> @@ -254,7 +257,10 @@ static void mhi_wwan_ctrl_stop(struct wwan_port *port)
>
>         cancel_work_sync(&mhiwwan->rx_refill);
>
> -       /* Send any pending DTR/RTS state before the channel stops */
> +       /* Try to send any pending DTR/RTS state before the channel stops. This
> +        * is best effort too, a send that has to be retried goes out from
> +        * dtr_work after the channel has stopped.
> +        */
>         flush_delayed_work(&mhiwwan->dtr_work);
>
>         mhi_unprepare_from_transfer(mhiwwan->mhi_dev);
> @@ -376,7 +382,7 @@ static void mhi_wwan_ctrl_remove(struct mhi_device *mhi_dev)
>         struct mhi_wwan_dev *mhiwwan = dev_get_drvdata(&mhi_dev->dev);
>
>         wwan_remove_port(mhiwwan->wwan_port);
> -       /* Give the DTR/RTS drop from removal one attempt, then stop the work */
> +       /* Give any pending DTR/RTS state a last attempt, then stop the work */
>         flush_delayed_work(&mhiwwan->dtr_work);
>         disable_delayed_work_sync(&mhiwwan->dtr_work);
>         kfree(mhiwwan);
> --
> 2.43.0
>