[PATCH] dmaengine: qcom: gpi: Set IEOB on linked I2C GO TRE to retire TX descriptor

[Vsevolod Nevorotov]

In GPI mode, an I2C read transaction consists of a command phase on the
TX channel (issuing CONFIG0 and GO TREs) linked to a data phase on the RX
channel (issuing the DMA TRE to receive data).

Commit 656147fb1d4c ("i2c: qcom-geni: Avoid extra TX DMA TRE for single
read message in GPI mode") avoided programming a dummy TX DMA TRE for read
messages, leaving only the GO TRE on the TX channel with the TRE_FLAGS_LINK
flag set.

However, gpi_create_i2c_tre() did not set TRE_FLAGS_IEOB (Interrupt on End
of Block) on the linked GO TRE. Because no TRE on the TX channel has an
interrupt flag set, GSI hardware never generates a completion event on
the TX channel when the GO command finishes. As a result, the TX transfer
ring read pointer is never advanced and TX descriptors are never retired.

Under sustained or high-frequency traffic (such as touchscreen controllers
operating at 120-240 Hz), the TX transfer ring quickly runs out of slots:
  gpi 900000.dma-controller: not enough space in ring, avail:1 required:3
  geni_i2c 990000.i2c: prep_slave_sg failed
  geni_i2c 990000.i2c: GPI transfer failed: -5

Fix this properly by setting TRE_FLAGS_IEOB on the GO TRE when multi_msg
is true (matching Qualcomm's hardware specification and the existing SPI
implementation in gpi_create_spi_tre). When the hardware finishes executing
the GO command block, it generates an MSM_GPI_TCE_EOB event on the TX
channel. In gpi_process_xfer_compl_event(), handle MSM_GPI_TCE_EOB for
linked I2C command descriptors without a subsequent TX DMA TRE by
retiring the descriptor and updating the cookie without invoking the
client callback, allowing the linked RX channel's DMA completion
(MSM_GPI_TCE_EOT) to signal final transfer completion to the client.
Other EOB events fall through to the default transfer completion path.

Fixes: 656147fb1d4c ("i2c: qcom-geni: Avoid extra TX DMA TRE for single read message in GPI mode")
Signed-off-by: Vsevolod Nevorotov <sevanevorotov29@xxxxxxxxx>
---
 drivers/dma/qcom/gpi.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/qcom/gpi.c b/drivers/dma/qcom/gpi.c
index a5055a6273a..a1ab63bf9f6 100644
--- a/drivers/dma/qcom/gpi.c
+++ b/drivers/dma/qcom/gpi.c
@@ -1050,6 +1050,13 @@ static void gpi_process_xfer_compl_event(struct gchan *gchan,
 			return;
 	}
 
+	if (compl_event->code == MSM_GPI_TCE_EOB &&
+	    gchan->protocol == QCOM_GPI_I2C &&
+	    (gpi_desc->tre[gpi_desc->num_tre - 1].dword[3] & TRE_FLAGS_LINK)) {
+		dma_cookie_complete(&vd->tx);
+		goto gpi_free_desc;
+	}
+
 	if (compl_event->code == MSM_GPI_TCE_UNEXP_ERR) {
 		dev_err(gpii->gpi_dev->dev, "Error in Transaction\n");
 		result.result = DMA_TRANS_ABORTED;
@@ -1668,10 +1675,12 @@ static int gpi_create_i2c_tre(struct gchan *chan, struct gpi_desc *desc,
 
 		tre->dword[3] = u32_encode_bits(TRE_TYPE_GO, TRE_FLAGS_TYPE);
 
-		if (i2c->multi_msg)
+		if (i2c->multi_msg) {
+			tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_IEOB);
 			tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_LINK);
-		else
+		} else {
 			tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_CHAIN);
+		}
 	}
 
 	if (i2c->op == I2C_READ || i2c->multi_msg == false) {
-- 
2.55.0