[PATCH v4 03/11] i3c: master: Extend address status bit to 4 and add I3C_ADDR_SLOT_EXT_INIT

[Frank Li <Frank.Li@nxp.com>]

Extend the address status bit to 4 and introduce the I3C_ADDR_SLOT_EXT_INIT
macro to indicate that a device prefers a specific address. This is
generally set by the 'assigned-address' in the device tree source (dts)
file.

 ┌────┬─────────────┬───┬─────────┬───┐
 │S/Sr│ 7'h7E RnW=0 │ACK│ ENTDAA  │ T ├────┐
 └────┴─────────────┴───┴─────────┴───┘    │
 ┌─────────────────────────────────────────┘
 │  ┌──┬─────────────┬───┬─────────────────┬────────────────┬───┬─────────┐
 └─►│Sr│7'h7E RnW=1  │ACK│48bit UID BCR DCR│Assign 7bit Addr│PAR│ ACK/NACK│
    └──┴─────────────┴───┴─────────────────┴────────────────┴───┴─────────┘

Some master controllers (such as HCI) need to prepare the entire above
transaction before sending it out to the I3C bus. This means that a 7-bit
dynamic address needs to be allocated before knowing the target device's
UID information.

However, some I3C targets want a specific address (called as
"init_dyn_addr"), which is typically specified by the DT's assigned-address
property. (Lower addresses have higher IBI priority, and the target can
adjust this by using the assigned-address property if using DT). The
function i3c_master_add_i3c_dev_locked() will switch to this
"init_dyn_addr" if it is not in use.

Therefore, i3c_bus_get_free_addr() should return a free address that has
not been claimed by any target devices as "init_dyn_addr" (indicated by
I3C_ADDR_SLOT_EXT_INIT). This allows the device with the "init_dyn_addr"
to switch to its "init_dyn_addr" when it hot-joins the I3C bus. Otherwise,
if the "init_dyn_addr" is already in use by another I3C device, the target
device will not be able to switch to its desired address.

If all of above address are already used, i3c_bus_get_free_addr() return
one from the claimed as init_dyn_addr and free address slot. This ensures
support devices as much as possible.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
change from v3 to v4
- rewrite commit message and comment for i3c_bus_get_free_addr()
---
 drivers/i3c/master.c       | 68 ++++++++++++++++++++++++++++++++++++++++------
 include/linux/i3c/master.h |  7 +++--
 2 files changed, 64 insertions(+), 11 deletions(-)

diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
index 2c9d45486ed8b..1dad727e28435 100644
--- a/drivers/i3c/master.c
+++ b/drivers/i3c/master.c
@@ -345,7 +345,7 @@ const struct bus_type i3c_bus_type = {
 EXPORT_SYMBOL_GPL(i3c_bus_type);
 
 static enum i3c_addr_slot_status
-i3c_bus_get_addr_slot_status(struct i3c_bus *bus, u16 addr)
+i3c_bus_get_addr_slot_status_ext(struct i3c_bus *bus, u16 addr)
 {
 	unsigned long status;
 	int bitpos = addr * I3C_ADDR_SLOT_STATUS_BITS;
@@ -356,11 +356,17 @@ i3c_bus_get_addr_slot_status(struct i3c_bus *bus, u16 addr)
 	status = bus->addrslots[bitpos / BITS_PER_LONG];
 	status >>= bitpos % BITS_PER_LONG;
 
-	return status & I3C_ADDR_SLOT_STATUS_MASK;
+	return status & I3C_ADDR_SLOT_EXT_STATUS_MASK;
 }
 
-static void i3c_bus_set_addr_slot_status(struct i3c_bus *bus, u16 addr,
-					 enum i3c_addr_slot_status status)
+static enum i3c_addr_slot_status
+i3c_bus_get_addr_slot_status(struct i3c_bus *bus, u16 addr)
+{
+	return i3c_bus_get_addr_slot_status_ext(bus, addr) & I3C_ADDR_SLOT_STATUS_MASK;
+}
+
+static void i3c_bus_set_addr_slot_status_mask(struct i3c_bus *bus, u16 addr,
+					      enum i3c_addr_slot_status status, int mask)
 {
 	int bitpos = addr * I3C_ADDR_SLOT_STATUS_BITS;
 	unsigned long *ptr;
@@ -369,11 +375,22 @@ static void i3c_bus_set_addr_slot_status(struct i3c_bus *bus, u16 addr,
 		return;
 
 	ptr = bus->addrslots + (bitpos / BITS_PER_LONG);
-	*ptr &= ~((unsigned long)I3C_ADDR_SLOT_STATUS_MASK <<
-						(bitpos % BITS_PER_LONG));
+	*ptr &= ~((unsigned long)mask << (bitpos % BITS_PER_LONG));
 	*ptr |= (unsigned long)status << (bitpos % BITS_PER_LONG);
 }
 
+static void i3c_bus_set_addr_slot_status(struct i3c_bus *bus, u16 addr,
+					 enum i3c_addr_slot_status status)
+{
+	i3c_bus_set_addr_slot_status_mask(bus, addr, status, I3C_ADDR_SLOT_STATUS_MASK);
+}
+
+static void i3c_bus_set_addr_slot_status_ext(struct i3c_bus *bus, u16 addr,
+					     enum i3c_addr_slot_status status)
+{
+	i3c_bus_set_addr_slot_status_mask(bus, addr, status, I3C_ADDR_SLOT_EXT_STATUS_MASK);
+}
+
 static bool i3c_bus_dev_addr_is_avail(struct i3c_bus *bus, u8 addr)
 {
 	enum i3c_addr_slot_status status;
@@ -383,11 +400,44 @@ static bool i3c_bus_dev_addr_is_avail(struct i3c_bus *bus, u8 addr)
 	return status == I3C_ADDR_SLOT_FREE;
 }
 
+/*
+ * ┌────┬─────────────┬───┬─────────┬───┐
+ * │S/Sr│ 7'h7E RnW=0 │ACK│ ENTDAA  │ T ├────┐
+ * └────┴─────────────┴───┴─────────┴───┘    │
+ * ┌─────────────────────────────────────────┘
+ * │  ┌──┬─────────────┬───┬─────────────────┬────────────────┬───┬─────────┐
+ * └─►│Sr│7'h7E RnW=1  │ACK│48bit UID BCR DCR│Assign 7bit Addr│PAR│ ACK/NACK│
+ *    └──┴─────────────┴───┴─────────────────┴────────────────┴───┴─────────┘
+ * Some master controllers (such as HCI) need to prepare the entire above transaction before
+ * sending it out to the I3C bus. This means that a 7-bit dynamic address needs to be allocated
+ * before knowing the target device's UID information.
+ *
+ * However, some I3C targets want a specific address (called as "init_dyn_addr"), which is
+ * typically specified by the DT's assigned-address property. (Lower addresses have higher IBI
+ * priority, and the target can adjust this by using the assigned-address property if using DT).
+ * The function i3c_master_add_i3c_dev_locked() will switch to this "init_dyn_addr" if it is not
+ * in use.
+ *
+ * Therefore, i3c_bus_get_free_addr() should return a free address that has not been claimed by any
+ * target devices as "init_dyn_addr". This allows the device with the "init_dyn_addr" to switch to
+ * its "init_dyn_addr" when it hot-joins the I3C bus. Otherwise, if the "init_dyn_addr" is already
+ * in use by another I3C device, the target device will not be able to switch to its desired
+ * address.
+ *
+ * If all of above address are already used, i3c_bus_get_free_addr() return one from the claimed as
+ * init_dyn_addr and free address slot. This ensures support devices as much as possible.
+ */
 static int i3c_bus_get_free_addr(struct i3c_bus *bus, u8 start_addr)
 {
 	enum i3c_addr_slot_status status;
 	u8 addr;
 
+	for (addr = start_addr; addr < I3C_MAX_ADDR; addr++) {
+		status = i3c_bus_get_addr_slot_status_ext(bus, addr);
+		if (status == I3C_ADDR_SLOT_FREE)
+			return addr;
+	}
+
 	for (addr = start_addr; addr < I3C_MAX_ADDR; addr++) {
 		status = i3c_bus_get_addr_slot_status(bus, addr);
 		if (status == I3C_ADDR_SLOT_FREE)
@@ -1906,9 +1956,9 @@ static int i3c_master_bus_init(struct i3c_master_controller *master)
 			goto err_rstdaa;
 		}
 
-		i3c_bus_set_addr_slot_status(&master->bus,
-					     i3cboardinfo->init_dyn_addr,
-					     I3C_ADDR_SLOT_I3C_DEV);
+		i3c_bus_set_addr_slot_status_ext(&master->bus,
+						 i3cboardinfo->init_dyn_addr,
+						 I3C_ADDR_SLOT_I3C_DEV | I3C_ADDR_SLOT_EXT_INIT);
 
 		/*
 		 * Only try to create/attach devices that have a static
diff --git a/include/linux/i3c/master.h b/include/linux/i3c/master.h
index 2fac4a45ec600..2c826d17eb571 100644
--- a/include/linux/i3c/master.h
+++ b/include/linux/i3c/master.h
@@ -284,7 +284,8 @@ enum i3c_bus_mode {
  * @I3C_ADDR_SLOT_I2C_DEV: address is assigned to an I2C device
  * @I3C_ADDR_SLOT_I3C_DEV: address is assigned to an I3C device
  * @I3C_ADDR_SLOT_STATUS_MASK: address slot mask
- *
+ * @I3C_ADDR_SLOT_EXT_INIT: the bitmask represents addresses that are preferred by some devices,
+ *			    such as the "assigned-address" property in a device tree source (DTS).
  * On an I3C bus, addresses are assigned dynamically, and we need to know which
  * addresses are free to use and which ones are already assigned.
  *
@@ -297,9 +298,11 @@ enum i3c_addr_slot_status {
 	I3C_ADDR_SLOT_I2C_DEV,
 	I3C_ADDR_SLOT_I3C_DEV,
 	I3C_ADDR_SLOT_STATUS_MASK = 3,
+	I3C_ADDR_SLOT_EXT_STATUS_MASK = 7,
+	I3C_ADDR_SLOT_EXT_INIT = BIT(2),
 };
 
-#define I3C_ADDR_SLOT_STATUS_BITS 2
+#define I3C_ADDR_SLOT_STATUS_BITS 4
 
 /**
  * struct i3c_bus - I3C bus object

-- 
2.34.1


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