[Huawei Ascend Mate 2] xordos:
CM12.1 support DPI adjustment natively (if you see some apps still show bigger font, then try modify the build.prop to same value, this may help.)

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B320/B322 update screwed up below DPI adjustment. Thanks [MENTION=5509156]medwatt[/MENTION] testing, see #45 for details. For values like 240 or 260, the phone is completely blank, and if you do 'adb shell logcat *:E', you can see the resource not found error all over the place. :(

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Edit on July 3, 2015:

On Lollipop B309, the ro.sf.lcd_density is in build.prop already and set to 320, we can change it to smaller value: (make a backup first)

ro.sf.lcd_density=240

you can use any number between 240 to 320. Save then reboot. (Thanks [MENTION=2667067]ArkAngel06[/MENTION] point out this entry still works)

Then everything is working fine. No expose needed and didn't see any big problem so far. :)

One problem we noticed is stock 'Browser' app FC, pls use your favorate 3rd party browser instead. (The one i currently use is boat browser)

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Following is original post for JellyBean 4.3

===Normal disclaims applies, be careful and know how to use adb to restore /system/build.prop before you try this=============

You phone may brick if this file got corrupted.

ROOT is required to change the LCD density.

Today trying to play around the DPI of display, and noticed the stock value is 320:

getprop | grep dens
[ro.sf.lcd_density]: [320]

But our 720p display native DPI is 240. That's why all the stuff display so big??

Anyway, I backed up /system/build.prop, and play a little bit.

I recommend simply use Root Browser with "RB Text Editor" to do the task. Other DPI changer app may work and convenient, but it is more risky and may do some change unknown to the phone. Due to lack of backup/restore recovery right now, I prefer manually editing the file myself.

Adding following to the end of /system/build.prop.

ro.sf.lcd_density=264

For some different varies like Consumer Cellular version, or MT2L05 version, you can try following if above doesn't work:

qemu.sf.lcd_density=264

Not sure it is a bug or what, when I use ES file explorer to edit the file, If I select edit mode right after open the file, it won't scroll to the end of file. I have to scroll to the end first in view mode, then select edit mode. Anyway, Root Browser editor works without any problem.

Following is some test result:

______________ System UI________ Settings__________ Gallery
180__________force close
200______________ok____________ force close______ force close
220______________ok____________ force close______ force close
240(native)______ok____________ force close______ force close
260______________ok____________ force close______ force close
264______________ok________________ ok____________force close
280______________ok________________ ok____________force close
320(stock)______ ok________________ ok________________ ok

Also, for all DPI less than 320, the stock lock screen shortcut is not displayed properly.

I think I will stick with 280 (update, now I am using 264) for a few days and see if I found more problems. And it should be easy to find an alternative gallery app.

The smaller font and everything actually make the display more clear and sharp :)

PS. I know there is font size in display settings, but the DPI change will make system zoom everything based on this new display density.

Thanks aragon257 and others feedback, some info from below is collected from the replies. Thanks.

MORE INFO/UPDATE:

. There is Exposed framework modules (like app settings) to do per app DPI settings. Please see end of this post for more info.

. The app force closing caused by lower DPI is purely software (view layout arrangement) issue, so lowering DPI will not do any harm to hardware.

. List of Apps that Force Close. I list them from higher DPI to lower DPI, The apps that crashes in higher DPI will also crash in lower DPI.

DPI 264 or 280: Currently I am using 264.

Lock Screen: No crash here. The app short cut moved to center of the circle, and requires less distance swipe to unlock.

Gallery (Also affecting camera since it start Gallery when you view pictures)

Alternative: "Galleray KK" and "Camera KK" from play store works pretty good, though it is Ads supported.

DPI 240:

Settings

Phone app when receiving calls.

Use Xposed Framework

OK, set DPI to 240 in build.prop, I need use Xposed module "App Settings" to set following App DPI to higher value to make the phone fully work:

Gallery(com.android.gallery3d): 297 (dp: 320x480)
Phone(com.android.phone): 264
Settings(com.android.settings): 264
SystemUI(com.android.systemui): 264

This number is set to lowest possible value, of course you can set to 320, then related apps will be bigger.

Please see attachment for some screenshot: (Left is stock 320 DPI, right is 264 DPI)