On Mon, Jan 06, 2014 at 10:57:14AM -0800, Doug Anderson wrote: > On Thu, Jan 2, 2014 at 4:25 PM, Luigi Semenzato <semenzato@xxxxxxxxxxxx> wrote: > > On Thu, Jan 2, 2014 at 11:48 AM, Dmitry Torokhov > > <dmitry.torokhov@xxxxxxxxx> wrote: > >> Hi Doug, > >> > >> On Thu, Jan 02, 2014 at 09:40:44AM -0800, Doug Anderson wrote: > >>> Dmitry, > >>> > >>> Thanks for cleaning up cros_eckeyb. :) I'm a little curious about > >>> the motivation here. I can't imagine a keyboard with all that many > >>> columns (ours has 13), so it's really not taking a whole lot off of > >>> the stack. Are you trying to make some sort of automated checker > >>> happy, or just generally trying to keep the kernel consistent? > >> > >> I compile most of the code with sparse so I prefer to keep it happy. > >> > >>> > >>> In any case, I'm not opposed to moving these bytes off the stack. > >>> Comments below, though... > >>> > >>> --- > >>> > >>> On Tue, Dec 31, 2013 at 11:35 AM, Dmitry Torokhov > >>> <dmitry.torokhov@xxxxxxxxx> wrote: > ... > >>> > @@ -217,32 +219,40 @@ static int cros_ec_keyb_probe(struct platform_device *pdev) > >>> > struct cros_ec_keyb *ckdev; > >>> > struct input_dev *idev; > >>> > struct device_node *np; > >>> > + unsigned int rows, cols; > >>> > + size_t size; > >>> > int err; > >>> > > >>> > np = pdev->dev.of_node; > >>> > if (!np) > >>> > return -ENODEV; > >>> > > >>> > - ckdev = devm_kzalloc(&pdev->dev, sizeof(*ckdev), GFP_KERNEL); > >>> > - if (!ckdev) > >>> > - return -ENOMEM; > >>> > - err = matrix_keypad_parse_of_params(&pdev->dev, &ckdev->rows, > >>> > - &ckdev->cols); > >>> > + err = matrix_keypad_parse_of_params(&pdev->dev, &rows, &cols); > >>> > if (err) > >>> > return err; > >>> > - ckdev->old_kb_state = devm_kzalloc(&pdev->dev, ckdev->cols, GFP_KERNEL); > >>> > - if (!ckdev->old_kb_state) > >>> > - return -ENOMEM; > >>> > > >>> > - idev = devm_input_allocate_device(&pdev->dev); > >>> > - if (!idev) > >>> > + /* > >>> > + * Double memory for keyboard state so we have space for storing > >>> > + * current and previous state. > >>> > + */ > >>> > + size = sizeof(*ckdev) + 2 * cols * sizeof(*ckdev->kb_state); > >>> > + ckdev = devm_kzalloc(&pdev->dev, size, GFP_KERNEL); > >>> > + if (!ckdev) > >>> > return -ENOMEM; > >>> > >>> This change seems like a lot of complexity to save one memory > >>> allocation. If you insist, I'd be OK with having one allocation for > >>> both buffers (kb_state and old_kb_state) but trying to jam this onto > >>> the end of the structure is non-obvious. It certainly took me a > >>> minute to understand what you were doing and why. > >> > >> It is not one additional allocation but more as you need to allocate > >> devres data structures and add them there. I think we have quite a few > >> drivers piggy-backing key tables at the end of data structures. > > OK, I will leave this as your call. To me, piggybacking like this > make sense if you've got a single chunk of dynamic memory that you > just want to cram onto the end of the structure. It just gets more > complicated when you have two nearly identical chunks of memory and > one of them is using this piggybacking technique while the other > isn't. > > What about a compromise and declaring as: > > u8 *kb_state; > u8 *old_kb_state; > u8 buffers[]; > > You still have the same number of memory allocations but (to me) it's > much clearer what's going on here. You do pay a penalty of an extra > memory dereference and an extra 4 bytes of memory, but clarity should > trump that. OK, I can do that. Thanks. -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
