On Fri, 06 Mar 2020 09:25:49 +0100, Hans de Goede wrote: > > Hi, > > On 3/6/20 8:59 AM, Takashi Iwai wrote: > > On Thu, 05 Mar 2020 15:33:04 +0100, > > Hans de Goede wrote: > >> > >> Hi, > >> > >> Because of a bug-report about power-saving related plops/clocks on a > >> Lenovo T470s, I've asked inside Red Hat if people with a T470s and > >> running a recent kernel were also experiencing this. > >> > >> Most people are happy with the audio, but I did get a few bug reports > >> about plops on the headphones-jack. > >> > >> One of the suggestions which I got from 2 different users is to > >> disable power-saving for the HDA driver when on AC, esp. since most > >> headphones-jack use (esp. with an external amplifier which amplifies > >> the problem) is done while the laptop is sitting on a desk and thus > >> typically is connected to a charger. > >> > >> I'm personally not necessarily a fan of changing settings based > >> on being connected to ac or not, but I guess that in this case > >> it might not be such a bad idea ? > > > > Actually the power-saving-toggle-on-demand used to be the standard > > behavior by some power management tools including some > > thinkpad-specific one, IIRC. So the behavior itself isn't too bad if > > the pop noise can't be fully eliminated. > > Right, atleast TLP does something like this, and maybe also some of > the Ubuntu pm scripts. But if we are going to do this I would like to > come up with some upstream, non 3th party (from a std gnu/linux > perspective), solution. > > Note upstream does not necessarily mean inside the kernel, it could be > e.g. part of systemd, e.g. a udev rule (not sure if that is possible) > or done by some pm suspend/resume hooks which are installed by default > (not sure if systemd's suspend code supports hooks though). > > If there is consensus that this is something which is a good idea / > a reasonable thing to do; and also consensus that this should be done > outside the kernel I can take a look at putting together a systemd > pull-req for this. I have a mixed feeling about introducing it in standard. The power-saving itself is always good no matter whether it's cabled or not, it's merely a workaround for the problem that couldn't be fully fixed in kernel side. So it was provided as an option for users who really need it. But it's certainly a feasible option. OTOH, I still wonder about the cause of the noise on Thinkpad. In general, if that comes from the codec power down (the Realtek one), it's usually fixable in a certain level. Or if it's at the power down of the link (power_save_controller option), it's often hard and we keep the blacklist. thanks, Takashi
