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Hans de Goede
Hi All,

Update: Thank you everyone for all the test-reports I've received. The response has been quite overwhelming, with over 50 test-reports received sofar. The results are all over the place, some people see no changes, some people report the aprox. 0.5W saving my own test show and many people also report display problems, sometimes combined with a significant increase in power-consumption. I need to take a closer look at all the results, but right now I believe that the best way forward with this is (unfortunately) a whitelist matching on a combination of panel-id (from edid) and dmi data, so that we can at least enable this on popular models (any model with atleast one user willing to contribute).

As you've probably read already I'm working on improving Linux laptop battery live, previously I've talked about enabling SATA link powermanagement by default. This is now enabled in rawhide / Fedora 28 since January 1st and so far no issues have been reported. This is really good news as this leads to significantly better idle power consumption (1 - 1.5W lower) on laptops with sata disks. Fedora 28 will also enable HDA codec autosuspend and autosuspend for USB Bluetooth controllers, for another (aprox) 0.8W gain.

But we're not done yet, testing on a Lenovo T440s and X240 has shown that enabling Panel Self Refresh (PSR) by setting i915.enable_psr=1 saves another 0.5W. Enabling this on all machines has been tried in the past and it causes problems on some machines. So we will likely need either a blacklist or whitelist for this. I'm leaning towards a whitelist to avoid regressions, but if there are say only 10-20 models which don't work with it a blacklist makes more sense. So the most important thing to do right now is gather more data, hence this blog post.

So I would like to ask everyone who runs Linux on their laptop (with a recent-ish kernel) to test this and gather some data for me:

  1. Check if your laptop uses an eDP panel, do: "ls /sys/class/drm" there should be a card?-eDP-1 there, if not your laptop is using LVDS or DSI for the panel, and this does not apply to your laptop.

  2. Check that your machine supports PSR, do: "cat /sys/kernel/debug/dri/0/i915_edp_psr_status", if this says: "PSR not supported", then this does not apply to your laptop.

  3. Get a baseline powerconsumption measurement, install powertop ("sudo dnf install powertop" on Fedora), then close all your apps except for 1 terminal, maximimze that terminal and run "sudo powertop". Unplug your laptop if plugged in and wait 5 minutes, on some laptops the power measurement is a moving average so this is necessary to get a reliable reading. Now look at the power consumption shown (e.g. 7.95W), watch it for a couple of refreshes as it sometimes spikes when something wakes up to do some work, write down the lowest value you see, this is our base value for your laptops power consumption, write this down.                        Note beware of "dim screen when idle" messing with your brightness, either make sure you do no touch the laptop for a couple of minutes before taking the reading, or turn this feature of in your power-settings.

  4. Add "i915.enable_psr=1" to your kernel cmdline and reboot, check that the LCD panel still works, try suspend/resume and blanking the screen (by e.g. locking it under GNOME3) still work.

  5. Check that psr actually is enabled now (you're panel might not support it), do: "cat /sys/kernel/debug/dri/0/i915_edp_psr_status" and check that it says both: "Enabled: yes" and  "Active: yes"

  6. Measure idle powerconsumption again as described under 1. Make sure you use the same LCD brightness setting as before, write down the new value

  7. Dump your LCD panels edid, run "cat /sys/class/drm/card0-eDP-1/edid > panel-edid"

  8. Send me a mail at hdegoede@redhat.com with the following in there:


  • Report of success or bad side effects

  • The idle powerconsumption before and after the changes

  • The brand and model of your laptop

  • The "panel-edid" file attached

  • The output of the following commands:

  • cat /proc/cpuinfo | grep "model name" | uniq

  • cat /sys/class/dmi/id/modalias

Once I've info from enough models hopefully I can come up with some way for us to enable PSR be default, or at least build a whitelist with popular laptop models and enable it there.

Thanks & Regards,

Hans