[PATCH 2/2] i2c: qcom-geni: Provide an option to disable DMA processing

[Lee Jones]

We have a production-level laptop (Lenovo Yoga C630) which is exhibiting
a rather horrific bug.  When I2C HID devices are being scanned for at
boot-time the QCom Geni based I2C (Serial Engine) attempts to use DMA.
When it does, the laptop reboots and the user never sees the OS.

The beautiful thing about this approach is that, *if* the Geni SE DMA
ever starts working, we can remove the C code and any old properties
left in older DTs just become NOOP.  Older kernels with newer DTs (less
of a priority) *still* will not work - but they do not work now anyway.

Fixes: 8bc529b25354 ("soc: qcom: geni: Add support for ACPI")
Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
Reviewed-by: Vinod Koul <vkoul@xxxxxxxxxx>
---
 drivers/i2c/busses/i2c-qcom-geni.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
index a89bfce5388e..8822dea82980 100644
--- a/drivers/i2c/busses/i2c-qcom-geni.c
+++ b/drivers/i2c/busses/i2c-qcom-geni.c
@@ -353,13 +353,16 @@ static void geni_i2c_tx_fsm_rst(struct geni_i2c_dev *gi2c)
 static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
 				u32 m_param)
 {
+	struct device_node *np = gi2c->se.dev->of_node;
 	dma_addr_t rx_dma;
 	unsigned long time_left;
-	void *dma_buf;
+	void *dma_buf = NULL;
 	struct geni_se *se = &gi2c->se;
 	size_t len = msg->len;
 
-	dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
+	if (!of_property_read_bool(np, "qcom,geni-se-no-dma"))
+		dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
+
 	if (dma_buf)
 		geni_se_select_mode(se, GENI_SE_DMA);
 	else
@@ -392,13 +395,16 @@ static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
 static int geni_i2c_tx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
 				u32 m_param)
 {
+	struct device_node *np = gi2c->se.dev->of_node;
 	dma_addr_t tx_dma;
 	unsigned long time_left;
-	void *dma_buf;
+	void *dma_buf = NULL;
 	struct geni_se *se = &gi2c->se;
 	size_t len = msg->len;
 
-	dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
+	if (!of_property_read_bool(np, "qcom,geni-se-no-dma"))
+		dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
+
 	if (dma_buf)
 		geni_se_select_mode(se, GENI_SE_DMA);
 	else
-- 
2.17.1