[PATCH 1/2] soundwire: Add a helper function to indicate a device will detach

[Charles Keepax]

SoundWire devices will sometimes need to reset themselves,
typical times might include when taking over the device to ensure
a consistent state or after downloading a firmware update to boot
into the new version. Often such a reset will also result in the
device detaching from the SoundWire bus, in this case the driver
has to be careful. Naively calling sdw_slave_wait_for_init()
after doing the reset could immediately succeed if the bus hasn't
seen the detach yet, causing the driver to proceed attempting
to communicate with the device whilst it is detached.

Add a helper function that a driver can call to indicate it is
about to initiate an action that will cause the device to detach
from the bus. This will reinit the completions in the peripheral
for device attach, ensuring that the next sdw_slave_wait_for_init()
will not complete before the detach has been seen by the core.

Signed-off-by: Charles Keepax <ckeepax@xxxxxxxxxxxxxxxxxxxxx>
---
 drivers/soundwire/bus.h       |  6 ------
 include/linux/soundwire/sdw.h | 29 +++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
index 44e4f51939176..59b6aee0ea6eb 100644
--- a/drivers/soundwire/bus.h
+++ b/drivers/soundwire/bus.h
@@ -231,12 +231,6 @@ static inline void sdw_fill_port_params(struct sdw_port_params *params,
 int sdw_bread_no_pm_unlocked(struct sdw_bus *bus, u16 dev_num, u32 addr);
 int sdw_bwrite_no_pm_unlocked(struct sdw_bus *bus, u16 dev_num, u32 addr, u8 value);
 
-/*
- * At the moment we only track Master-initiated hw_reset.
- * Additional fields can be added as needed
- */
-#define SDW_UNATTACH_REQUEST_MASTER_RESET	BIT(0)
-
 void sdw_clear_slave_status(struct sdw_bus *bus, u32 request);
 int sdw_slave_modalias(const struct sdw_slave *slave, char *buf, size_t size);
 void sdw_compute_slave_ports(struct sdw_master_runtime *m_rt,
diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
index 707ca6bd1e23d..969604755ce41 100644
--- a/include/linux/soundwire/sdw.h
+++ b/include/linux/soundwire/sdw.h
@@ -25,6 +25,13 @@ struct device_node;
 struct sdw_bus;
 struct sdw_slave;
 
+/*
+ * At the moment we only track Master-initiated/Slave-initiated hw_reset.
+ * Additional fields can be added as needed
+ */
+#define SDW_UNATTACH_REQUEST_MASTER_RESET	BIT(0)
+#define SDW_UNATTACH_REQUEST_SLAVE_RESET	BIT(1)
+
 /* SDW spec defines and enums, as defined by MIPI 1.1. Spec */
 
 /* SDW Broadcast Device Number */
@@ -1214,6 +1221,28 @@ static inline int sdw_update_no_pm(struct sdw_slave *slave, u32 addr, u8 mask, u
 
 #endif /* CONFIG_SOUNDWIRE */
 
+/**
+ * sdw_slave_signal_unattach - Signal that the peripheral is about to detach
+ * @slave: Pointer to the SoundWire peripheral.
+ * @timeout_us: Timeout in microseconds.
+ *
+ * Inform the core that the peripheral is about to detach from the bus, this
+ * is usually due to some implementation defined reset mechanism. After this
+ * sdw_slave_wait_for_init() should be called to wait for the device to
+ * return.
+ *
+ * Return: Zero on success, and a negative error code on failure.
+ */
+static inline void sdw_slave_signal_unattach(struct sdw_slave *slave)
+{
+	if (!slave)
+		return;
+
+	slave->unattach_request = SDW_UNATTACH_REQUEST_SLAVE_RESET;
+	reinit_completion(&slave->enumeration_complete);
+	reinit_completion(&slave->initialization_complete);
+}
+
 /**
  * sdw_slave_wait_for_init - Wait for device initialisation
  * @slave: Pointer to the SoundWire peripheral.
-- 
2.47.3