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

[Marc Gonzalez <marc.w.gonzalez@free.fr>]

[ Trimming recipients list for idle chat ]

On 05/09/2019 09:52, Lee Jones wrote:

> 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@linaro.org>
> Reviewed-by: Vinod Koul <vkoul@kernel.org>
> ---
>  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
> 

Would it make sense to factorize the DT lookup within a helper?
(For example; not compile-tested; not sure it's worth it)

diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
index a89bfce5388e..1489181f60fe 100644
--- a/drivers/i2c/busses/i2c-qcom-geni.c
+++ b/drivers/i2c/busses/i2c-qcom-geni.c
@@ -350,6 +350,14 @@ static void geni_i2c_tx_fsm_rst(struct geni_i2c_dev *gi2c)
 		dev_err(gi2c->se.dev, "Timeout resetting TX_FSM\n");
 }
 
+static void *get_dma_buf(struct geni_se *se, struct i2c_msg *msg)
+{
+	if (of_property_read_bool(se->dev->of_node, "qcom,geni-se-no-dma"))
+		return NULL;
+
+	return i2c_get_dma_safe_msg_buf(msg, 32);
+}
+
 static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
 				u32 m_param)
 {
@@ -359,7 +367,7 @@ static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
 	struct geni_se *se = &gi2c->se;
 	size_t len = msg->len;
 
-	dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
+	dma_buf = get_dma_buf(se, msg);
 	if (dma_buf)
 		geni_se_select_mode(se, GENI_SE_DMA);
 	else
@@ -398,7 +406,7 @@ static int geni_i2c_tx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
 	struct geni_se *se = &gi2c->se;
 	size_t len = msg->len;
 
-	dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
+	dma_buf = get_dma_buf(se, msg);
 	if (dma_buf)
 		geni_se_select_mode(se, GENI_SE_DMA);
 	else