linux-kernel - [V3] i2c: i2c-qcom-geni: Correct I2C TRE sequence

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Date: Thu,  1 Feb 2024 15:43:23 +0530
From: Viken Dadhaniya <quic_vdadhani@...cinc.com>
To: andersson@...nel.org, konrad.dybcio@...aro.org, andi.shyti@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, vkoul@...nel.org,
        quic_bjorande@...cinc.com, manivannan.sadhasivam@...aro.org,
        bryan.odonoghue@...aro.org
Cc: quic_msavaliy@...cinc.com, quic_vtanuku@...cinc.com,
        Viken Dadhaniya <quic_vdadhani@...cinc.com>
Subject: [V3] i2c: i2c-qcom-geni: Correct I2C TRE sequence

For i2c read operation in GSI mode, we are getting timeout
due to malformed TRE basically incorrect TRE sequence
in gpi(drivers/dma/qcom/gpi.c) driver.

TRE stands for Transfer Ring Element - which is basically an element with
size of 4 words. It contains all information like slave address,
clk divider, dma address value data size etc).

Mainly we have 3 TREs(Config, GO and DMA tre).
- CONFIG TRE : consists of internal register configuration which is
               required before start of the transfer.
- DMA TRE :    contains DDR/Memory address, called as DMA descriptor.
- GO TRE :     contains Transfer directions, slave ID, Delay flags, Length
               of the transfer.

Driver calls GPI driver API to config each TRE depending on the protocol.
If we see GPI driver, for RX operation we are configuring DMA tre and
for TX operation we are configuring GO tre.

For read operation tre sequence will be as below which is not aligned
to hardware programming guide.

- CONFIG tre
- DMA tre
- GO tre

As per Qualcomm's internal Hardware Programming Guide, we should configure
TREs in below sequence for any RX only transfer.

- CONFIG tre
- GO tre
- DMA tre

In summary, for RX only transfers, we are reordering DMA and GO TREs.
Tested covering i2c read/write transfer on QCM6490 RB3 board.

Fixes: d8703554f4de ("i2c: qcom-geni: Add support for GPI DMA")
Signed-off-by: Viken Dadhaniya <quic_vdadhani@...cinc.com>
---
v2 -> v3:
- Update commit log to explain change in simple way.
- Correct fix tag format.

v1 -> v2:
- Remove redundant check.
- update commit log.
- add fix tag.
---
---
 drivers/i2c/busses/i2c-qcom-geni.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
index 0d2e7171e3a6..da94df466e83 100644
--- a/drivers/i2c/busses/i2c-qcom-geni.c
+++ b/drivers/i2c/busses/i2c-qcom-geni.c
@@ -613,20 +613,20 @@ static int geni_i2c_gpi_xfer(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[], i
 
 		peripheral.addr = msgs[i].addr;
 
+		ret =  geni_i2c_gpi(gi2c, &msgs[i], &config,
+				    &tx_addr, &tx_buf, I2C_WRITE, gi2c->tx_c);
+		if (ret)
+			goto err;
+
 		if (msgs[i].flags & I2C_M_RD) {
 			ret =  geni_i2c_gpi(gi2c, &msgs[i], &config,
 					    &rx_addr, &rx_buf, I2C_READ, gi2c->rx_c);
 			if (ret)
 				goto err;
-		}
-
-		ret =  geni_i2c_gpi(gi2c, &msgs[i], &config,
-				    &tx_addr, &tx_buf, I2C_WRITE, gi2c->tx_c);
-		if (ret)
-			goto err;
 
-		if (msgs[i].flags & I2C_M_RD)
 			dma_async_issue_pending(gi2c->rx_c);
+		}
+
 		dma_async_issue_pending(gi2c->tx_c);
 
 		timeout = wait_for_completion_timeout(&gi2c->done, XFER_TIMEOUT);
-- 
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