[PATCH 0/1] soundwire: bus: Fix for missing UNATTACH when re-enumerating
This is an alternative fix for the race where a device that is reset can be found on #0 and its ID reprogrammed before the bus code has handled a PING showing it unattached.
The other possible fix is here: https://lore.kernel.org/all/20220825122241.273090-4-rf@opensource.cirrus.com...
Richard Fitzgerald (1): soundwire: bus: Don't re-enumerate before status is UNATTACHED
drivers/soundwire/bus.c | 7 +++++++ 1 file changed, 7 insertions(+)
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@opensource.cirrus.com --- drivers/soundwire/bus.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c index cb77da84a4f9..a3d3d66b3410 100644 --- a/drivers/soundwire/bus.c +++ b/drivers/soundwire/bus.c @@ -766,6 +766,13 @@ static int sdw_program_device_num(struct sdw_bus *bus) if (sdw_compare_devid(slave, id) == 0) { found = true;
+ /* + * Don't re-enumerate a device until we've seen + * it UNATTACH. + */ + if (slave->status != SDW_SLAVE_UNATTACHED) + break; + /* * Assign a new dev_num to this Slave and * not mark it present. It will be marked
On 29/08/2022 10:44, 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@opensource.cirrus.com
drivers/soundwire/bus.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c index cb77da84a4f9..a3d3d66b3410 100644 --- a/drivers/soundwire/bus.c +++ b/drivers/soundwire/bus.c @@ -766,6 +766,13 @@ static int sdw_program_device_num(struct sdw_bus *bus) if (sdw_compare_devid(slave, id) == 0) { found = true;
/** Don't re-enumerate a device until we've seen* it UNATTACH.*/if (slave->status != SDW_SLAVE_UNATTACHED)break;
This should return. We're going to keep seeing this peripheral as the next to be enumerated until we program its device ID.
/* * Assign a new dev_num to this Slave and * not mark it present. It will be marked
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Richard Fitzgerald