Hi Aniroop, On Thu, Nov 20, 2014 at 01:31:44AM +0530, Aniroop Mathur wrote: > Dear Mr. Torokhov, > Greetings of the day ! :) > > Recently, I saw input_allocate_device() funtion in input.c file and > faced one small doubt about it. > Unfortunately, I could not find the decent answer on internet. Can you > help to answer the query as follows: > > In this function, input_no is initialized to 0. > static atomic_t input_no = ATOMIC_INIT(0); > and then it is used to set input device name like below: > dev_set_name(&dev->dev, "input%ld", (unsigned long) > atomic_inc_return(&input_no) - 1); > > Here, we are increamenting input no by 1 and then again decreamenting by 1. > I think, it is because we have initialized input_no to 0 and we want > name of input devices to start from input0. > > Is it not a good idea to initialize input_no to -1 and then only > increamenting input_no without subtracting when setting input device > name ? > With this, we will be able to save one extra subtraction instruction > every time input device is allocated. Historically atomic_t on sparc32 had only 24 usable bits so I think setting it to -1 would not have worked. Now it is no longer a concern, but neither that extra subtraction is expensive so nobody bothered to change it. 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
