Bug 431057

Created attachment 134462 [details]
Video

Please watch the video.

The video shows:
1. The display at 1920×1080@60, which I try to switch to 3840×2160@39.98
2. Display Configuration shows 60/50/30/25/24 Hz options for 3840×2160, switches to 30 Hz when 50 Hz is selected
3. After leaving configuration and entering it again, it shows correct 30/40 Hz for 3840×2160
4. Trying to switch from 3840×2160@30 to 1920×1080@60. Display Configuration shows 40/30 Hz for 1920×1080, switches to 30 Hz interlaced when none refresh rate is selected.
5. After leaving configuration and entering it again, it shows correct 60/50/30/25/24 Hz options for 1920×1080

Created attachment 134464 [details]
kscreen-console json

The output of kscreen-console json

It seems that Display Configuration applet is built on incorrect assumption that all resolution will have common refresh rates. It does not update refresh rates on resolution change, refreshRates() function accepts only output (screen) as a single argument.

Unfortunately the issue is still present in the newest KDE 5.22.4.

Thank you for the bug report. Unfortunately we were not able to get to it yet. Can we ask you to please see if you can reproduce the issue with Plasma 5.25 or 5.26?

If you can, please change the status to CONFIRMED when replying. Thanks a lot!

(In reply to Nate Graham from comment #5)
> Thank you for the bug report. Unfortunately we were not able to get to it
> yet. Can we ask you to please see if you can reproduce the issue with Plasma
> 5.25 or 5.26?
> 
> If you can, please change the status to CONFIRMED when replying. Thanks a
> lot!

This is still an issue as of KDE 5.25.4 on Fedora 35.

Based on the attachment, it appears that the issue is that the refresh rates are stored as floats, like:

> "refreshRate": 120.10496520996094,
> "refreshRate": 120.00162506103516,

That's not gonna work. We are losing precision so anything that tries to compare one to another will get a result of false.

I'm in favor of changing config format. Let's store framerate as a string which is a fixed point number with two decimal digits. Exactly two should be enough to distinguish any valid modes, e.g.
- 640x480 @ 59.94 vs 59.93;
- 1920x1080 @ 59.94 vs 60.00;

note: this isn't a problem for [1280x720 @ 50.00] vs [720x576 @ 50.00], because in this case resolution is different.

If there are legit two modes with same resolution but with refresh rate only diverting at or after third decimal digit, then I'd assume it doesn't matter which to pick up.

> Based on the attachment, it appears that the issue is that the refresh rates are stored as floats, like:

>> "refreshRate": 120.10496520996094,
>> "refreshRate": 120.00162506103516,

> That's not gonna work. We are losing precision so anything that tries to compare one to another will get a result of false.

As a workaround, I could implement a fuzzy lookup, such that a mode with the closest value to the one loaded from config will be picked up, iff absolute delta is less than 1Hz.

+1 for storing as fixed point with two decimal places at the very minimum.

*** Bug 502764 has been marked as a duplicate of this bug. ***

(In reply to Nate Graham from comment #9)
> +1 for storing as fixed point with two decimal places at the very minimum.

It's basically what everyone else does. Round to two decimal places.

On my Dell Inspiron 5770, with its built-in 2K display the refesh rate is shown as: 60.01 Hz.
kscreen-doctor -o shows:
Output: 1 eDP-1 1c060aa7-39a3-419d-95c2-12addc2a9006
        enabled
        connected
        priority 1
        Panel
        replication source:0
        Modes:  1:1920x1080@60.01*!  2:1920x1080@48.01  3:1280x1024@59.90  4:1280x1024@59.90  5:1024x768@59.92  6:1024x768@59.92  7:1280x800@59.81  8:1280x800@59.81  9:1600x900@59.95  10:1600x900@59.95  11:1368x768@59.88  12:1368x768@59.88  13:1280x720@59.85  14:1280x720@59.85 
        Geometry: 0,0 1600x900
        Scale: 1.2
        Rotation: 1
        Overscan: 0
        Vrr: incapable
        RgbRange: Full
        HDR: incapable
        Wide Color Gamut: incapable
        ICC profile: none
        Color profile source: sRGB
        Color power preference: prefer efficiency and performance
        Brightness control: supported, set to 97% and dimming to 100%
        Color resolution: automatic (10), range: [6; 12] bits per color
        Allow EDR: always
        Sharpness control: unsupported
Info Center's EDID page shows:
# card0-eDP-1 #######################
Block 0, Base EDID:
  EDID Structure Version & Revision: 1.4
  Vendor & Product Identification:
    Manufacturer: CMN
    Model: 5944
    Made in: week 43 of 2015
  Basic Display Parameters & Features:
    Digital display
    Bits per primary color channel: 6
    DisplayPort interface
    Maximum image size: 38 cm x 21 cm
    Gamma: 2.20
    Supported color formats: RGB 4:4:4
    First detailed timing includes the native pixel format and preferred refresh rate
  Color Characteristics:
    Red  : 0.6464, 0.3378
    Green: 0.3164, 0.6142
    Blue : 0.1572, 0.0439
    White: 0.3134, 0.3291
  Established Timings I & II: none
  Standard Timings: none
  Detailed Timing Descriptors:
    DTD 1:  1920x1080   60.007852 Hz  16:9     67.929 kHz    152.840000 MHz (381 mm x 214 mm)
                 Hfront   48 Hsync  32 Hback  250 Hpol P
                 Vfront    3 Vsync   5 Vback   44 Vpol N
    DTD 2:  1920x1080   48.005497 Hz  16:9     54.342 kHz    122.270000 MHz (381 mm x 214 mm)
                 Hfront   48 Hsync  32 Hback  250 Hpol P
                 Vfront    3 Vsync   5 Vback   44 Vpol N
    Alphanumeric Data String: 'N1YPX�173HCE'
Checksum: 0x08

----------------

EDID conformity: PASS

So in my case the rounding to only 2 decimal places is not that good, I mean nice to see.
I would rather see just 60 Hz or  the full 60.007852 Hz
Or just 60 Hz, but with a way to also see the more precise version, other than looking at the EDID.
Anyway, I wanted mainly just to report what I'm seeing on my laptop (the GPU is an Intel UHD 620, if that helps).
I'm using Debian 14 (Forky, AKA the 'testing' repository), Linux 6.17, Mesa 25.3, Plasma 6.5.4, Frameworks 6.20.