New issue
Advanced search Search tips

Issue 718585 link

Starred by 1 user
Status: Available
Owner: ----
Cc:
bleung@chromium.org
derat@chromium.org
tbroch@chromium.org
Components:
EstimatedDays: ----
NextAction: ----
OS: Chrome
Pri: 3
Type: Feature



Sign in to add a comment

Do not brighten screen on AC insert if charger falls into "Low-power charger" category

Project Member Reported by williscalkins@chromium.org, May 4 2017 
In ChromeOS devices with Type-C charging, on AC insert, the UI typically brightens the screen because there is no longer a power consumption concern and the screen backlight is a major power consumer (up to 5 watts).

However, a Low-power charger cannot always sustain this system power.  Low power chargers range from 2.5-7.5 watts.  Brightening the screen could be the difference between charging and discharging.

We should only raise the brightness of the screen if plugged into a high power Type-C charger.

If we want to get fancy we can actually look at the battery charge rate, but I think differentiating based on the "Low power charger" signal already in the UI, it will be a clear, simple distinction.

Comment 1 by derat@chromium.org, May 4 2017

Cc: derat@chromium.org bleung@chromium.org
Before we consider doing this, someone should should audit our classification of low-power chargers. Right now, we set powerd's usb_min_ac_watts pref to 20 W on all devices, which is wrong.

Also note that enterprise policies currently define different behavior for "AC" and "battery" power. This two-way split is present through powerd. While it's possible to have a one-off difference to support a third state for the sake of choosing the backlight brightness, it'll make the code more confusing.

Do you have some numbers measuring the difference in power draw between the default AC and battery brightnesses on the device(s) you're concerned about?

Comment 2 by tbroch@chromium.org, Jun 10 2017

Cc: tbroch@chromium.org
Status: Available (was: Untriaged)
Agreed 20W for everything is a bit too simplistic.  

Some slightly less simplistic approaches might be,
1. Look at the UMA battery discharge data for type-C platforms and adjust usb_min_ac_watts per-platform based on that.
- What percentile would we choose?  90 to catch most users?  What about platform power improvements / regressions 

2. We could also pick a default per-platform based on some known assumptions.
- charge full design / 10 == Wavg on battery for average user
- Scale this number to account for AC->DC charging loss
- Scale again by delta between AC vs DC display brightness

However in general I think we may need to step back and decide what we want to communicate to the user w/ respect to low battery chargers before investing much time in this.

Devil's advocate for this case how do I assume that charging is more important than brightness for a given user?

Finally, at least on one recent platform we decided to forgo backlight transitions based on AC or DC.  That keeps the planet greener and makes this a 'wont-fix'
Project Member

Comment 3 by sheriffbot@chromium.org, Jun 11 2018

Labels: Hotlist-Recharge-Cold
Status: Untriaged (was: Available)
This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Comment 4 by tbroch@chromium.org, Jul 20

Status: Available (was: Untriaged)
►

Sign in to add a comment