linux-kernel - Re: [PATCH 4/4] Input: zforce - reduce stack memory allocated to frames

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Date:	Mon, 27 Jan 2014 21:22:39 +0100
From:	Heiko Stübner <heiko@...ech.de>
To:	Luis Ortega <luiorpe1@....es>
Cc:	dmitry.torokhov@...il.com, yongjun_wei@...ndmicro.com.cn,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] Input: zforce - reduce stack memory allocated to frames

On Monday, 27. January 2014 19:46:13 Luis Ortega wrote:
> A frame is a u8 array with the following structure:
> [PAYLOAD_HEADER, PAYLOAD_LENGTH, ...PAYLOAD_BODY...]
> 
> PAYLOAD_BODY can be at most 255 bytes long, as it's size is represented
> by PAYLOAD_LENGTH. Therefore we can reduce the stack memory allocated to
> payload_buffer[] roughly by half, from 512 to 257 bytes.

Nice catch, thanks

Acked-by: Heiko Stuebner <heiko@...ech.de>

on a bq Cervantes (imx6sl)
Tested-by: Heiko Stuebner <heiko@...ech.de>


As a side-note, this change conflicts with one of my patches adding devicetree 
support to the driver [0], which Dmitry will hopefully also look at soon.

So one of us might need to respin his series depending on the ordering.



[0] http://permalink.gmane.org/gmane.linux.kernel.input/33587




> 
> Signed-off-by: Luis Ortega <luiorpe1@....es>
> ---
>  drivers/input/touchscreen/zforce_ts.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/input/touchscreen/zforce_ts.c
> b/drivers/input/touchscreen/zforce_ts.c index e082d5c..afb2492 100644
> --- a/drivers/input/touchscreen/zforce_ts.c
> +++ b/drivers/input/touchscreen/zforce_ts.c
> @@ -33,6 +33,7 @@
>  #define WAIT_TIMEOUT		msecs_to_jiffies(1000)
> 
>  #define FRAME_START		0xee
> +#define FRAME_MAXSIZE		257
> 
>  /* Offsets of the different parts of the payload the controller sends */
>  #define PAYLOAD_HEADER		0
> @@ -475,7 +476,7 @@ static irqreturn_t zforce_irq_thread(int irq, void
> *dev_id) struct i2c_client *client = ts->client;
>  	const struct zforce_ts_platdata *pdata = dev_get_platdata(&client->dev);
>  	int ret;
> -	u8 payload_buffer[512];
> +	u8 payload_buffer[FRAME_MAXSIZE];
>  	u8 *payload;
> 
>  	/*

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