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

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Message-ID: <20181011001114.GA173303@dtor-ws>
Date:   Wed, 10 Oct 2018 17:11:14 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH v2] Input: elants_i2c - Use DMA safe i2c when possible

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@...-dreams.de>
> Signed-off-by: Stephen Boyd <swboyd@...omium.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