ASPEED AST2700 SOC is a 64 bits quad core CPUs (Cortex-a35)
and the base address of dram is "0x4 00000000" which
is 64bits address.

The AST2700 support the maximum DRAM size is 8 GB.
The DRAM physical address range is from "0x4_0000_0000" to
"0x5_FFFF_FFFF".

The DRAM offset range is from "0x0_0000_0000" to
"0x1_FFFF_FFFF" and it is enough to use bits [33:0]
saving the dram offset.

Therefore, save the high part physical address bit[1:0]
of Tx/Rx buffer address as dma_dram_offset bit[33:32].
It does not need to decrease the dram physical
high part address for DMA operation.
(high part physical address bit[7:0] – 4)

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
---
 hw/i2c/aspeed_i2c.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/hw/i2c/aspeed_i2c.c b/hw/i2c/aspeed_i2c.c
index c1ff80b1cf..44c3c39233 100644
--- a/hw/i2c/aspeed_i2c.c
+++ b/hw/i2c/aspeed_i2c.c
@@ -743,6 +743,14 @@ static void aspeed_i2c_bus_new_write(AspeedI2CBus *bus, hwaddr offset,
                       __func__);
         break;
 
+    /*
+     * The AST2700 support the maximum DRAM size is 8 GB.
+     * The DRAM offset range is from 0x0_0000_0000 to
+     * 0x1_FFFF_FFFF and it is enough to use bits [33:0]
+     * saving the dram offset.
+     * Therefore, save the high part physical address bit[1:0]
+     * of Tx/Rx buffer address as dma_dram_offset bit[33:32].
+     */
     case A_I2CM_DMA_TX_ADDR_HI:
         if (!aic->has_dma64) {
             qemu_log_mask(LOG_GUEST_ERROR, "%s: No DMA 64 bits support\n",
@@ -752,6 +760,8 @@ static void aspeed_i2c_bus_new_write(AspeedI2CBus *bus, hwaddr offset,
         bus->regs[R_I2CM_DMA_TX_ADDR_HI] = FIELD_EX32(value,
                                                       I2CM_DMA_TX_ADDR_HI,
                                                       ADDR_HI);
+        bus->dma_dram_offset = deposit64(bus->dma_dram_offset, 32, 32,
+                                         extract32(value, 0, 2));
         break;
     case A_I2CM_DMA_RX_ADDR_HI:
         if (!aic->has_dma64) {
@@ -762,6 +772,8 @@ static void aspeed_i2c_bus_new_write(AspeedI2CBus *bus, hwaddr offset,
         bus->regs[R_I2CM_DMA_RX_ADDR_HI] = FIELD_EX32(value,
                                                       I2CM_DMA_RX_ADDR_HI,
                                                       ADDR_HI);
+        bus->dma_dram_offset = deposit64(bus->dma_dram_offset, 32, 32,
+                                         extract32(value, 0, 2));
         break;
     case A_I2CS_DMA_TX_ADDR_HI:
         qemu_log_mask(LOG_UNIMP,
@@ -777,6 +789,8 @@ static void aspeed_i2c_bus_new_write(AspeedI2CBus *bus, hwaddr offset,
         bus->regs[R_I2CS_DMA_RX_ADDR_HI] = FIELD_EX32(value,
                                                       I2CS_DMA_RX_ADDR_HI,
                                                       ADDR_HI);
+        bus->dma_dram_offset = deposit64(bus->dma_dram_offset, 32, 32,
+                                         extract32(value, 0, 2));
         break;
     default:
         qemu_log_mask(LOG_GUEST_ERROR, "%s: Bad offset 0x%" HWADDR_PRIx "\n",
-- 
2.34.1