> -----Original Message----- > From: Dmitry Torokhov [mailto:dmitry.torokhov@xxxxxxxxx] > Sent: 05 June, 2015 20:12 > To: Tirdea, Irina > Cc: 'Antonio Ospite'; Bastien Nocera; linux-input@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 2/9] input: goodix: fix variable length array warning > > On Fri, Jun 05, 2015 at 05:00:05PM +0000, Tirdea, Irina wrote: > > > > > > > -----Original Message----- > > > From: Dmitry Torokhov [mailto:dmitry.torokhov@xxxxxxxxx] > > > Sent: 05 June, 2015 19:41 > > > To: Tirdea, Irina > > > Cc: 'Antonio Ospite'; Bastien Nocera; linux-input@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > > > Subject: Re: [PATCH 2/9] input: goodix: fix variable length array warning > > > > > > On Fri, Jun 05, 2015 at 04:34:38PM +0000, Tirdea, Irina wrote: > > > > > > > > > > > > > -----Original Message----- > > > > > From: linux-input-owner@xxxxxxxxxxxxxxx [mailto:linux-input-owner@xxxxxxxxxxxxxxx] On Behalf Of Antonio Ospite > > > > > Sent: 03 June, 2015 23:50 > > > > > To: Tirdea, Irina > > > > > Cc: Dmitry Torokhov; Bastien Nocera; linux-input@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > > > > > Subject: Re: [PATCH 2/9] input: goodix: fix variable length array warning > > > > > > > > > > On Wed, 3 Jun 2015 10:26:47 +0000 > > > > > "Tirdea, Irina" <irina.tirdea@xxxxxxxxx> wrote: > > > > > > > > > > > > -----Original Message----- > > > > > > > From: Antonio Ospite [mailto:ao2@xxxxxx] > > > > > > > Sent: 28 May, 2015 18:58 > > > > > > > To: Tirdea, Irina > > > > > > > Cc: Dmitry Torokhov; Bastien Nocera; linux-input@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx > > > > > > > Subject: Re: [PATCH 2/9] input: goodix: fix variable length array warning > > > > > > > > > > > > > > On Thu, 28 May 2015 15:47:38 +0300 > > > > > > > Irina Tirdea <irina.tirdea@xxxxxxxxx> wrote: > > > > > > > > > > > > > > > Fix sparse warning: > > > > > > > > drivers/input/touchscreen/goodix.c:182:26: warning: > > > > > > > > Variable length array is used. > > > > > > > > > > > > > > > > Replace the variable length array with fixed length. > > > > > > > > > > > > > > > > Signed-off-by: Irina Tirdea <irina.tirdea@xxxxxxxxx> > > > > > > > > --- > > > > > > > > drivers/input/touchscreen/goodix.c | 2 +- > > > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/drivers/input/touchscreen/goodix.c b/drivers/input/touchscreen/goodix.c > > > > > > > > index c2e785c..dac1b3c 100644 > > > > > > > > --- a/drivers/input/touchscreen/goodix.c > > > > > > > > +++ b/drivers/input/touchscreen/goodix.c > > > > > > > > @@ -147,7 +147,7 @@ static void goodix_ts_report_touch(struct goodix_ts_data *ts, u8 *coor_data) > > > > > > > > */ > > > > > > > > static void goodix_process_events(struct goodix_ts_data *ts) > > > > > > > > { > > > > > > > > - u8 point_data[1 + GOODIX_CONTACT_SIZE * ts->max_touch_num]; > > > > > > > > + u8 point_data[1 + GOODIX_CONTACT_SIZE * GOODIX_MAX_CONTACTS]; > > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > > > > > > Hi Antonio, > > > > > > > > > > > > > this fixes the warning from sparse, but also changes the semantics of > > > > > > > the code: ts->max_touch_num is less that GOODIX_MAX_CONTACTS for 5 > > > > > > > touches devices and in this case we'll end up using more memory than is > > > > > > > necessary. > > > > > > > > > > > > > > > > > > > I wasn't sure if it is better to save the 5 bytes or fix the warning, > > > > > > so I sent this to get some more input. > > > > > > Thanks for the feedback, I will drop this patch. > > > > > > > > > > > > > > > > Use kmalloc() or, alternatively, add at least a comment telling why you > > > > > think that sacrificing a few bytes —only for some devices— has > > > > > advantages over dynamic allocation. > > > > > > > > > > > > > You are right, kmalloc will solve both problems - the sparse warning and allocating > > > > more bytes than necessary. Don't know why I did not think of that. > > > > Will use that in v2. > > > > > > Please leave the patch as is. We can spare 80 bytes on the stack given > > > that we are running in threaded IRQ. kmallocing will use more code and > > > runtime resources and won't give any benefits. > > > > I was actually thinking of allocating it with devm_kzalloc just once at device init and > > storing a pointer to it in the goodix_ts_data structure. > > Still, why? Even if you do this once you will need both code and runtime > resources to bookkeeping whereas allocating 80 bytes on stack are just a > matter of register addition. And because we are running in threaded IRQ > context there is no concern of blowing up the limited stack. > > The story would be different if you needed, let's say 800 or 1600 bytes. > Ok, I see your point. Will leave the patch as is. Thanks, Irina > Thanks. > > -- > Dmitry ��.n��������+%������w��{.n����z�{��ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
