On Mon, Aug 23, 2021 at 3:51 PM Nuno Sá <noname.nuno@xxxxxxxxx> wrote: > On Mon, 2021-08-23 at 14:14 +0300, Andy Shevchenko wrote: > > On Fri, Aug 20, 2021 at 9:53 AM Nuno Sá <nuno.sa@xxxxxxxxxx> wrote: > > > Check if an optional reset gpio is present and if so, make sure to > > > reset > > > the device. > > > > ... > > > > > + usleep_range(1000, 1005); > > > > The delta should be at least 20%, otherwise I'm not sure why such a > > strict range? > > > > No special reason... I just had no hard requirement for delta so I just > gave something small. Is 20% documented anywhere? Quick search shows nothing, but I remember I saw it somewhere. So, the explanation is empirical, because the idea behind is to allow less HRT interrupts. When you do a tough margin, you may generate too many interrupts from the timer. So, 20% seems like a good balance for most of the values. The parameters to take into account are: - minimum (or maybe rather median?) CPU frequency the code will be run on - minimal sleep (for small sleeps even better to have udelay() as I believe documented in timers.rst, for bigger sleeps, like 10ms the margin can be 10% or so) - NO_HZ kernel configuration - etc (if anything I forgot) > I did a quick look on > the API's and I could not find nothing related. Anyways, if that is a > best practise for being more power friendly I'm happy to change it... > (well, we might end up just having 100ms here which means 'msleep()'). -- With Best Regards, Andy Shevchenko
