[PATCH v2] Input: elants_i2c - Use DMA safe i2c when possible

[PATCH v2] Input: elants_i2c - Use DMA safe i2c when possible

[Stephen Boyd]

This irq handler is always reading bytes from the device into a
kmalloced buffer, so it's safe to mark this transaction as DMA safe.
This avoids bouncing the buffer when an i2c controller decides to use
DMA for a transaction.

Cc: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---

Changes from v1:
 * Moved buf to end of structure to keep it cacheline aligned and DMA
   safe

 drivers/input/touchscreen/elants_i2c.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/input/touchscreen/elants_i2c.c b/drivers/input/touchscreen/elants_i2c.c
index d21ca39b0fdb..f2cb23121833 100644
--- a/drivers/input/touchscreen/elants_i2c.c
+++ b/drivers/input/touchscreen/elants_i2c.c
@@ -147,10 +147,11 @@ struct elants_data {
 	u8 cmd_resp[HEADER_SIZE];
 	struct completion cmd_done;
 
-	u8 buf[MAX_PACKET_SIZE];
-
 	bool wake_irq_enabled;
 	bool keep_power_in_suspend;
+
+	/* Must be last to be used for DMA operations */
+	u8 buf[MAX_PACKET_SIZE] ____cacheline_aligned;
 };
 
 static int elants_i2c_send(struct i2c_client *client,
@@ -863,7 +864,7 @@ static irqreturn_t elants_i2c_irq(int irq, void *_dev)
 	int i;
 	int len;
 
-	len = i2c_master_recv(client, ts->buf, sizeof(ts->buf));
+	len = i2c_master_recv_dmasafe(client, ts->buf, sizeof(ts->buf));
 	if (len < 0) {
 		dev_err(&client->dev, "%s: failed to read data: %d\n",
 			__func__, len);
-- 
Sent by a computer through tubes

Re: [PATCH v2] Input: elants_i2c - Use DMA safe i2c when possible

[Dmitry Torokhov]

On Wed, Oct 10, 2018 at 01:00:17PM -0700, Stephen Boyd wrote:
> This irq handler is always reading bytes from the device into a
> kmalloced buffer, so it's safe to mark this transaction as DMA safe.
> This avoids bouncing the buffer when an i2c controller decides to use
> DMA for a transaction.
> 
> Cc: Wolfram Sang <wsa@the-dreams.de>
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>

Changed patch description a bit (now that we are actually making the
buffer DMA-safe) and applied, thank you.

> ---
> 
> Changes from v1:
>  * Moved buf to end of structure to keep it cacheline aligned and DMA
>    safe
> 
>  drivers/input/touchscreen/elants_i2c.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/elants_i2c.c b/drivers/input/touchscreen/elants_i2c.c
> index d21ca39b0fdb..f2cb23121833 100644
> --- a/drivers/input/touchscreen/elants_i2c.c
> +++ b/drivers/input/touchscreen/elants_i2c.c
> @@ -147,10 +147,11 @@ struct elants_data {
>  	u8 cmd_resp[HEADER_SIZE];
>  	struct completion cmd_done;
>  
> -	u8 buf[MAX_PACKET_SIZE];
> -
>  	bool wake_irq_enabled;
>  	bool keep_power_in_suspend;
> +
> +	/* Must be last to be used for DMA operations */
> +	u8 buf[MAX_PACKET_SIZE] ____cacheline_aligned;
>  };
>  
>  static int elants_i2c_send(struct i2c_client *client,
> @@ -863,7 +864,7 @@ static irqreturn_t elants_i2c_irq(int irq, void *_dev)
>  	int i;
>  	int len;
>  
> -	len = i2c_master_recv(client, ts->buf, sizeof(ts->buf));
> +	len = i2c_master_recv_dmasafe(client, ts->buf, sizeof(ts->buf));
>  	if (len < 0) {
>  		dev_err(&client->dev, "%s: failed to read data: %d\n",
>  			__func__, len);
> -- 
> Sent by a computer through tubes
> 

-- 
Dmitry

Re: [PATCH v2] Input: elants_i2c - Use DMA safe i2c when possible

[Wolfram Sang]

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On Wed, Oct 10, 2018 at 01:00:17PM -0700, Stephen Boyd wrote:
> This irq handler is always reading bytes from the device into a
> kmalloced buffer, so it's safe to mark this transaction as DMA safe.
> This avoids bouncing the buffer when an i2c controller decides to use
> DMA for a transaction.
> 
> Cc: Wolfram Sang <wsa@the-dreams.de>
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>

For the record:

Acked-by: Wolfram Sang <wsa@the-dreams.de>


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