[PATCH 3/8] hw/i2c: smbus: increase MAX_DATA_LEN

The 32 byte payload was raised to 255 for block reads in the SMBus 3.0
specification. SMBus does not provide a way for devices to declare which
version of the spec they are designed to so we must allow newer devices
to return as much data as they allow.

vsmstate_smbus_extended_data is added to avoid breaking migration.

Specification: https://smbus.org/specs/SMBus_3_3_20240512.pdf

> 6.5.7 Block Write/Read
The Block Write begins with a slave address and a write condition. After the command code the host issues a byte count which describes how many more bytes will follow in the message. If a slave has 20 bytes to send, the byte count field will have the value 20 (14h), followed by the 20 bytes of data. The byte count does not include the PEC byte. The byte count may be 0. A Block Read or Block Write is allowed to transfer a maximum of 255 data bytes.

Signed-off-by: Titus Rwantare <[email protected]>
---
 hw/i2c/smbus_slave.c         | 27 ++++++++++++++++++++++++++-
 include/hw/i2c/smbus_slave.h |  2 +-
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/hw/i2c/smbus_slave.c b/hw/i2c/smbus_slave.c
index cfb61c879e..5dd2c38af7 100644
--- a/hw/i2c/smbus_slave.c
+++ b/hw/i2c/smbus_slave.c
@@ -215,6 +215,26 @@ bool smbus_vmstate_needed(SMBusDevice *dev)
     return dev->mode != SMBUS_IDLE;
 }
 
+#define SMBUS_DATA_MAX_LEN_OLD    34
+static bool smbus_extended_needed(void *opaque)
+{
+    SMBusDevice *dev = opaque;
+    return dev->data_len > SMBUS_DATA_MAX_LEN_OLD;
+}
+
+static const VMStateDescription vmstate_smbus_extended_data = {
+    .name = TYPE_SMBUS_DEVICE"/extended",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = smbus_extended_needed,
+    .fields = (const VMStateField[]) {
+        /* separately save [34..257) */
+        VMSTATE_UINT8_SUB_ARRAY(data_buf, SMBusDevice, SMBUS_DATA_MAX_LEN_OLD,
+            SMBUS_DATA_MAX_LEN - SMBUS_DATA_MAX_LEN_OLD),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 const VMStateDescription vmstate_smbus_device = {
     .name = TYPE_SMBUS_DEVICE,
     .version_id = 1,
@@ -223,8 +243,13 @@ const VMStateDescription vmstate_smbus_device = {
         VMSTATE_I2C_SLAVE(i2c, SMBusDevice),
         VMSTATE_INT32(mode, SMBusDevice),
         VMSTATE_INT32(data_len, SMBusDevice),
-        VMSTATE_UINT8_ARRAY(data_buf, SMBusDevice, SMBUS_DATA_MAX_LEN),
+        VMSTATE_UINT8_SUB_ARRAY(data_buf, SMBusDevice, 0,
+            SMBUS_DATA_MAX_LEN_OLD),
         VMSTATE_END_OF_LIST()
+    },
+    .subsections = (const VMStateDescription * const[]) {
+        &vmstate_smbus_extended_data,
+        NULL
     }
 };
 
diff --git a/include/hw/i2c/smbus_slave.h b/include/hw/i2c/smbus_slave.h
index 86bfe0a79e..59522ff1b1 100644
--- a/include/hw/i2c/smbus_slave.h
+++ b/include/hw/i2c/smbus_slave.h
@@ -64,7 +64,7 @@ struct SMBusDeviceClass {
     uint8_t (*receive_byte)(SMBusDevice *dev);
 };
 
-#define SMBUS_DATA_MAX_LEN 34  /* command + len + 32 bytes of data.  */
+#define SMBUS_DATA_MAX_LEN 257  /* command + len + 255 bytes of data.  */
 
 struct SMBusDevice {
     /* The SMBus protocol is implemented on top of I2C.  */
-- 
2.55.0.508.g3f0d502094-goog