On 9/7/22 10:52, Richard Fitzgerald wrote:
> Don't re-enumerate a peripheral on #0 until we have seen and
> handled an UNATTACHED notification for that peripheral.
>
> Without this, it is possible for the UNATTACHED status to be missed
> and so the slave->status remains at ATTACHED. If slave->status never
> changes to UNATTACHED the child driver will never be notified of the
> UNATTACH, and the code in sdw_handle_slave_status() will skip the
> second part of enumeration because the slave->status has not changed.
>
> This scenario can happen because PINGs are handled in a workqueue
> function which is working from a snapshot of an old PING, and there
> is no guarantee when this function will run.
>
> A peripheral could report attached in the PING being handled by
> sdw_handle_slave_status(), but has since reverted to device #0 and is
> then found in the loop in sdw_program_device_num(). Previously the
> code would not have updated slave->status to UNATTACHED because it had
> not yet handled a PING where that peripheral had UNATTACHED.
>
> This situation happens fairly frequently with multiple peripherals on
> a bus that are intentionally reset (for example after downloading
> firmware).
>
> Signed-off-by: Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
> ---
> drivers/soundwire/bus.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
> index 1cc858b4107d..6e569a875a9b 100644
> --- a/drivers/soundwire/bus.c
> +++ b/drivers/soundwire/bus.c
> @@ -773,6 +773,16 @@ static int sdw_program_device_num(struct sdw_bus *bus)
> if (sdw_compare_devid(slave, id) == 0) {
> found = true;
>
> + /*
> + * To prevent skipping state-machine stages don't
> + * program a device until we've seen it UNATTACH.
> + * Must return here because no other device on #0
> + * can be detected until this one has been
> + * assigned a device ID.
> + */
> + if (slave->status != SDW_SLAVE_UNATTACHED)
> + return 0;
> +
> /*
> * Assign a new dev_num to this Slave and
> * not mark it present. It will be marked
