Hi, Andy, On Thu, 2018-01-25 at 14:28 +0200, Andy Shevchenko wrote: > On Thu, 2018-01-25 at 16:12 +0800, Zhang Rui wrote: > > > > The .prepare() callback of intel-lpss driver does nothing but wakes > > up > > its > > children. I don't know if there is any reason to do so, but to me, > > this is > > not preferred because it should be the child device driver to do so > > when > > necessary, not the parent device driver. > > Plus, .prepare() does not support asynchronization. > > > > For example, on MS Surface Pro 4, there are 4 intel-lpss devices > > which > > are runtime suspended before system suspend, resuming each of them > > takes > > more than 100 milliseconds. Thus the .prepare() of intel-lpss > > driver > > takes > > 400ms+ on my surface pro 4, and I've seen platforms with 16 intel > > lpss > > devices. > > > > With this patch applied, the child devices are resumed in the > > .suspend() > > stage of the child device, and they are done in parallel, thus only > > 100ms > > is needed, no matter how many intel lpss devices there are. > > > > I have tested it on three different platforms and didn't find any > > obvious > > problem caused by this patch, and it indeed reduces the suspend > > time a > > lot. > > > > @@ -482,17 +482,6 @@ static int resume_lpss_device(struct device > > *dev, > > - device_for_each_child_reverse(dev, NULL, > > resume_lpss_device); > Besides introduced compiler warning, did you check the latest linux- > pm > changes? > > commit 8425ec7faff005500aad89b9fc00e5ba91ac57b9 > Author: Rafael J. Wysocki <[email protected]> > Date: Wed Jan 3 01:34:53 2018 +0100 > > PM / mfd: intel-lpss: Use DPM_FLAG_SMART_SUSPEND > No, thanks for the pointer, I will check this.
BTW, is there any reason that we need this .prepare() callback? thanks, rui
