hw/i2c: support multiple masters

Allow slaves to master the bus by registering a bottom halve. If the bus
is busy, the bottom half is queued up. When a slave has succesfully
mastered the bus, the bottom half is scheduled.

Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
[ clg : - fixed typos in commit log ]
Message-Id: <20220601210831.67259-4-its@irrelevant.dk>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20220630045133.32251-5-me@pjd.dev>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

1 files changed, 33 insertions, 1 deletions

diff --git a/hw/i2c/core.c b/hw/i2c/core.c
index d0cb2d32fa..145dce6078 100644
--- a/hw/i2c/core.c
+++ b/hw/i2c/core.c
@@ -13,6 +13,7 @@
 #include "migration/vmstate.h"
 #include "qapi/error.h"
 #include "qemu/module.h"
+#include "qemu/main-loop.h"
 #include "trace.h"
 
 #define I2C_BROADCAST 0x00
@@ -62,6 +63,7 @@ I2CBus *i2c_init_bus(DeviceState *parent, const char *name)
 
     bus = I2C_BUS(qbus_new(TYPE_I2C_BUS, parent, name));
     QLIST_INIT(&bus->current_devs);
+    QSIMPLEQ_INIT(&bus->pending_masters);
     vmstate_register(NULL, VMSTATE_INSTANCE_ID_ANY, &vmstate_i2c_bus, bus);
     return bus;
 }
@@ -74,7 +76,7 @@ void i2c_slave_set_address(I2CSlave *dev, uint8_t address)
 /* Return nonzero if bus is busy.  */
 int i2c_bus_busy(I2CBus *bus)
 {
-    return !QLIST_EMPTY(&bus->current_devs);
+    return !QLIST_EMPTY(&bus->current_devs) || bus->bh;
 }
 
 bool i2c_scan_bus(I2CBus *bus, uint8_t address, bool broadcast,
@@ -180,6 +182,26 @@ int i2c_start_transfer(I2CBus *bus, uint8_t address, bool is_recv)
                                                : I2C_START_SEND);
 }
 
+void i2c_bus_master(I2CBus *bus, QEMUBH *bh)
+{
+    if (i2c_bus_busy(bus)) {
+        I2CPendingMaster *node = g_new(struct I2CPendingMaster, 1);
+        node->bh = bh;
+
+        QSIMPLEQ_INSERT_TAIL(&bus->pending_masters, node, entry);
+
+        return;
+    }
+
+    bus->bh = bh;
+    qemu_bh_schedule(bus->bh);
+}
+
+void i2c_bus_release(I2CBus *bus)
+{
+    bus->bh = NULL;
+}
+
 int i2c_start_recv(I2CBus *bus, uint8_t address)
 {
     return i2c_do_start_transfer(bus, address, I2C_START_RECV);
@@ -206,6 +228,16 @@ void i2c_end_transfer(I2CBus *bus)
         g_free(node);
     }
     bus->broadcast = false;
+
+    if (!QSIMPLEQ_EMPTY(&bus->pending_masters)) {
+        I2CPendingMaster *node = QSIMPLEQ_FIRST(&bus->pending_masters);
+        bus->bh = node->bh;
+
+        QSIMPLEQ_REMOVE_HEAD(&bus->pending_masters, entry);
+        g_free(node);
+
+        qemu_bh_schedule(bus->bh);
+    }
 }
 
 int i2c_send(I2CBus *bus, uint8_t data)