[PATCH v2 4/8] i2c/aspeed: Fix DMA receive first-byte handling for block reads

An SMBus block read (I2C_M_RECV_LEN) reads the block length from the
first received byte. The Linux/U-Boot aspeed I2C driver obtains that
first byte from the I2CC_STS_AND_BUFF register (modelled here as
reg_byte_buf), even when the transfer uses DMA. The DMA receive path,
however, only wrote received data to DRAM and never updated
reg_byte_buf, so block reads read a stale/zero length.

Mirror the first DMA-received byte into reg_byte_buf so that
I2C_M_RECV_LEN transfers using DMA report the correct block length.
This is required for the ucd9000 driver, which uses
i2c_smbus_read_block_data().

Signed-off-by: Mikail Sadic <[email protected]>
---
 hw/i2c/aspeed_i2c.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/i2c/aspeed_i2c.c b/hw/i2c/aspeed_i2c.c
index 27afcaecee..facb54d27e 100644
--- a/hw/i2c/aspeed_i2c.c
+++ b/hw/i2c/aspeed_i2c.c
@@ -365,6 +365,7 @@ static void aspeed_i2c_bus_recv(AspeedI2CBus *bus)
     uint32_t reg_pool_ctrl = aspeed_i2c_bus_pool_ctrl_offset(bus);
     uint32_t reg_byte_buf = aspeed_i2c_bus_byte_buf_offset(bus);
     uint32_t reg_dma_len = aspeed_i2c_bus_dma_len_offset(bus);
+    bool first_dma_byte;
     int pool_rx_count = SHARED_ARRAY_FIELD_EX32(bus->regs, reg_pool_ctrl,
                                                 RX_SIZE) + 1;
 
@@ -391,6 +392,7 @@ static void aspeed_i2c_bus_recv(AspeedI2CBus *bus)
         }
 
         aspeed_i2c_set_rx_dma_dram_offset(bus);
+        first_dma_byte = true;
         while (bus->regs[reg_dma_len]) {
             MemTxResult result;
 
@@ -407,6 +409,11 @@ static void aspeed_i2c_bus_recv(AspeedI2CBus *bus)
                 return;
             }
 
+            /* Mirror first byte to reg_byte_buf for I2C_M_RECV_LEN. */
+            if (first_dma_byte) {
+                SHARED_ARRAY_FIELD_DP32(bus->regs, reg_byte_buf, RX_BUF, data);
+                first_dma_byte = false;
+            }
             bus->dma_dram_offset++;
             bus->regs[reg_dma_len]--;
             /* In new mode, keep track of how many bytes we RXed */
-- 
2.53.0