How init.rc setprop works

Question

I have android 8 from nxp and using it on sabresd board. I am trying to change dpi settings through setprop settings So I have put this iside init.${hardware}.rc on boot event

# Set the density to 160dpi, default 128dpi is not good
# Set the density to 128 dpi for 480x800, 7 inch.
 setprop ro.sf.lcd_density 128

The device works fine and if I do this

wm density
Physical density:128

Now I put this dpi setting in kernel command line

androidboot.sf.lcd_density=128

but I do not see device to be in 128 dpi setting. Also

wm density
Physical density:160

Now this baffles me.Who gave 160dpi settings?

1. How putting setprop in init.$hardware.rc affects the display but not in kernel command line.

2. Who really processes setprop. I tried putting prints like this

   on boot
   exec /system/bin/echo "Trigger test E"

I saw nothing, so does that mean boot event never happened?

Answer 1

In android framework there is a file called

display file

that contains default dpi if none is specified.

This file have this setting,

public static final int DENSITY_MEDIUM = 160;

Which is used if no dpi is specified.