[PATCH] drivers: input: touchscreen: sur40: use static variable instead of stack varialbe for 'packet_id'

[PATCH] drivers: input: touchscreen: sur40: use static variable instead of stack varialbe for 'packet_id'

[Chen Gang]

'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@gmail.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;
 
 	struct sur40_header *header = &sur40->bulk_in_buffer->header;
 	struct sur40_blob *inblob = &sur40->bulk_in_buffer->blobs[0];
-- 
1.7.7.6

Re: [PATCH] drivers: input: touchscreen: sur40: use static variable instead of stack varialbe for 'packet_id'

[Dmitry Torokhov]

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@gmail.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

Re: [PATCH] drivers: input: touchscreen: sur40: use static variable instead of stack varialbe for 'packet_id'

[Chen Gang]

On 11/28/2013 12:07 PM, Dmitry Torokhov wrote:
> 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@gmail.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().

OK, thanks, I will/should send patch v2 for it.

-- 
Chen Gang

[PATCH v2] drivers: input: touchscreen: sur40: remove stack variable 'packet_id' from sur40_poll()

[Chen Gang]

The drivers process all blobs in one pass, so there is no need to
preserve value of packet_id between calls to sur40_poll().

And the original implementation may cause 'packet_id' uninitialized,
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@gmail.com>
---
 drivers/input/touchscreen/sur40.c |   10 ----------
 1 files changed, 0 insertions(+), 10 deletions(-)

diff --git a/drivers/input/touchscreen/sur40.c b/drivers/input/touchscreen/sur40.c
index cfd1b7e..2ca32cb 100644
--- a/drivers/input/touchscreen/sur40.c
+++ b/drivers/input/touchscreen/sur40.c
@@ -251,7 +251,6 @@ 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;
 
 	struct sur40_header *header = &sur40->bulk_in_buffer->header;
 	struct sur40_blob *inblob = &sur40->bulk_in_buffer->blobs[0];
@@ -286,17 +285,8 @@ static void sur40_poll(struct input_polled_dev *polldev)
 		if (need_blobs == -1) {
 			need_blobs = le16_to_cpu(header->count);
 			dev_dbg(sur40->dev, "need %d blobs\n", need_blobs);
-			packet_id = header->packet_id;
 		}
 
-		/*
-		 * Sanity check. when video data is also being retrieved, the
-		 * packet ID will usually increase in the middle of a series
-		 * instead of at the end.
-		 */
-		if (packet_id != header->packet_id)
-			dev_warn(sur40->dev, "packet ID mismatch\n");
-
 		packet_blobs = result / sizeof(struct sur40_blob);
 		dev_dbg(sur40->dev, "received %d blobs\n", packet_blobs);
 
-- 
1.7.7.6