DC dimming is being enabled on the Huawei P30 and P30 Pro via a software update that is currently rolling out in China. This means that Huawei’s flagships have joined the growing number of phones with OLED screens that ditched PWM for DC dimming.
What’s the difference? In short, PWM rapidly turns the pixels on and off to lower the brightness - hence the name "pulse width modulation". This leads to a flicker that some people are sensitive to and causes headaches for them.
DC dimming reduces the current sent to each pixel, which reduces its brightness while keeping it on constantly (so, no flicker). It’s not quite as simple, however, because the color emitted by OLEDs tends to shift at low currents meaning makers need to compensate for this (otherwise, the color accuracy of the screen goes out the window).
According to the change log, DC dimming mode is enabled by a toggle in the settings. This update (all 400MB of it) also optimizes the in-display fingerprint reader.
There's no word on whether DC dimming will be enabled on older Huawei flagships.
Source (in Chinese)