linux-kernel - Re: [PATCH] drivers: input: touchscreen: sur40: use static variable instead of stack varialbe for 'packet

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Date:	Wed, 27 Nov 2013 20:07:41 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Chen Gang <gang.chen.5i5j@...il.com>
Cc:	floe@...terbrot.org, rydberg@...omail.se,
	David Herrmann <dh.herrmann@...il.com>,
	rkuo <rkuo@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-input@...r.kernel.org
Subject: Re: [PATCH] drivers: input: touchscreen: sur40: use static variable
 instead of stack varialbe for 'packet_id'

Hi Chen,

On Wed, Nov 27, 2013 at 10:15:33AM +0800, Chen Gang wrote:
> 'packet_id' is used for checking sequence whether in order, it need be
> static variable independent from sur40_poll().
> 
> The related warning (with allmodconfig under hexagon):
> 
>   drivers/input/touchscreen/sur40.c: In function 'sur40_poll':
>   drivers/input/touchscreen/sur40.c:297:6: warning: 'packet_id' may be used uninitialized in this function [-Wuninitialized]
> 
> 
> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
> ---
>  drivers/input/touchscreen/sur40.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/sur40.c b/drivers/input/touchscreen/sur40.c
> index cfd1b7e..5dfd01a 100644
> --- a/drivers/input/touchscreen/sur40.c
> +++ b/drivers/input/touchscreen/sur40.c
> @@ -251,7 +251,7 @@ static void sur40_poll(struct input_polled_dev *polldev)
>  	struct sur40_state *sur40 = polldev->private;
>  	struct input_dev *input = polldev->input;
>  	int result, bulk_read, need_blobs, packet_blobs, i;
> -	u32 packet_id;
> +	static u32 packet_id;

It is usually not a good idea to use statics in device drivers as it
does not work well when you have several devices of the same type
present in a system. Also, we process all blobs in one pass so there is
no need to preserve value of packet_id between calls to sur40_poll().

Thanks.

-- 
Dmitry
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