[PATCH 2/8] hw/i2c: only schedule pending master when bus is idle

["Cédric Le Goater" <clg@kaod.org>]

From: Klaus Jensen <k.jensen@samsung.com>

It is not given that the current master will release the bus after a
transfer ends. Only schedule a pending master if the bus is idle.

Fixes: 37fa5ca42623 ("hw/i2c: support multiple masters")
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
Acked-by: Corey Minyard <cminyard@mvista.com>
Message-Id: <20221116084312.35808-2-its@irrelevant.dk>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 include/hw/i2c/i2c.h |  2 ++
 hw/i2c/aspeed_i2c.c  |  2 ++
 hw/i2c/core.c        | 37 ++++++++++++++++++++++---------------
 3 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/include/hw/i2c/i2c.h b/include/hw/i2c/i2c.h
index 9b9581d230..2a3abacd1b 100644
--- a/include/hw/i2c/i2c.h
+++ b/include/hw/i2c/i2c.h
@@ -141,6 +141,8 @@ int i2c_start_send(I2CBus *bus, uint8_t address);
  */
 int i2c_start_send_async(I2CBus *bus, uint8_t address);
 
+void i2c_schedule_pending_master(I2CBus *bus);
+
 void i2c_end_transfer(I2CBus *bus);
 void i2c_nack(I2CBus *bus);
 void i2c_ack(I2CBus *bus);
diff --git a/hw/i2c/aspeed_i2c.c b/hw/i2c/aspeed_i2c.c
index c166fd20fa..1f071a3811 100644
--- a/hw/i2c/aspeed_i2c.c
+++ b/hw/i2c/aspeed_i2c.c
@@ -550,6 +550,8 @@ static void aspeed_i2c_bus_handle_cmd(AspeedI2CBus *bus, uint64_t value)
         }
         SHARED_ARRAY_FIELD_DP32(bus->regs, reg_cmd, M_STOP_CMD, 0);
         aspeed_i2c_set_state(bus, I2CD_IDLE);
+
+        i2c_schedule_pending_master(bus->bus);
     }
 
     if (aspeed_i2c_bus_pkt_mode_en(bus)) {
diff --git a/hw/i2c/core.c b/hw/i2c/core.c
index d4ba8146bf..bed594fe59 100644
--- a/hw/i2c/core.c
+++ b/hw/i2c/core.c
@@ -185,22 +185,39 @@ int i2c_start_transfer(I2CBus *bus, uint8_t address, bool is_recv)
 
 void i2c_bus_master(I2CBus *bus, QEMUBH *bh)
 {
-    if (i2c_bus_busy(bus)) {
-        I2CPendingMaster *node = g_new(struct I2CPendingMaster, 1);
-        node->bh = bh;
+    I2CPendingMaster *node = g_new(struct I2CPendingMaster, 1);
+    node->bh = bh;
+
+    QSIMPLEQ_INSERT_TAIL(&bus->pending_masters, node, entry);
+}
+
+void i2c_schedule_pending_master(I2CBus *bus)
+{
+    I2CPendingMaster *node;
 
-        QSIMPLEQ_INSERT_TAIL(&bus->pending_masters, node, entry);
+    if (i2c_bus_busy(bus)) {
+        /* someone is already controlling the bus; wait for it to release it */
+        return;
+    }
 
+    if (QSIMPLEQ_EMPTY(&bus->pending_masters)) {
         return;
     }
 
-    bus->bh = bh;
+    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);
 }
 
 void i2c_bus_release(I2CBus *bus)
 {
     bus->bh = NULL;
+
+    i2c_schedule_pending_master(bus);
 }
 
 int i2c_start_recv(I2CBus *bus, uint8_t address)
@@ -234,16 +251,6 @@ 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)
-- 
2.39.1