Bug in kernel 5.3 - no GPU powersaving (i915 module has no RC6 powerstate)

My laptop shows in powertop (idle tab) GPU power on 100%. RC6 or other energy saving states 0%. I check my old laptop - it was different there. Reading about it I found the parameter enable_rc6. It was "1" at my old laptop - but not at all available with my new one. (Core m5 Skylake, Ubuntu 18.04 Mate - old laptop same Ubuntu but N3530).

Edit:
(I repeated test installing Linux Mint Mate 19.03 - also an Ubuntu kernel - With initial Kernel 5.0 it was working. Rc6 was used most of the time. After the update to Kernel 5.3, this disappeared. So it seems to be a regression of the new Kernel).

:~$ modinfo -p i915
modeset:Use kernel modesetting [KMS] (0=disable, 1=on, -1=force vga console preference [default]) (int)
enable_dc:Enable power-saving display C-states. (-1=auto [default]; 0=disable; 1=up to DC5; 2=up to DC6) (int)
enable_fbc:Enable frame buffer compression for power savings (default: -1 (use per-chip default)) (int)
lvds_channel_mode:Specify LVDS channel mode (0=probe BIOS [default], 1=single-channel, 2=dual-channel) (int)
panel_use_ssc:Use Spread Spectrum Clock with panels [LVDS/eDP] (default: auto from VBT) (int)
vbt_sdvo_panel_type:Override/Ignore selection of SDVO panel mode in the VBT (-2=ignore, -1=auto [default], index in VBT BIOS table) (int)
reset:Attempt GPU resets (0=disabled, 1=full gpu reset, 2=engine reset [default]) (int)
vbt_firmware:Load VBT from specified file under /lib/firmware (charp)
error_capture:Record the GPU state following a hang. This information in /sys/class/drm/card<N>/error is vital for triaging and debugging hangs. (bool)
enable_hangcheck:Periodically check GPU activity for detecting hangs. WARNING: Disabling this can cause system wide hangs. (default: true) (bool)
enable_psr:Enable PSR (0=disabled, 1=enabled) Default: -1 (use per-chip default) (int)
force_probe:Force probe the driver for specified devices. See CONFIG_DRM_I915_FORCE_PROBE for details. (charp)
alpha_support:Deprecated. See i915.force_probe. (bool)
disable_power_well:Disable display power wells when possible (-1=auto [default], 0=power wells always on, 1=power wells disabled when possible) (int)
enable_ips:Enable IPS (default: true) (int)
fastboot:Try to skip unnecessary mode sets at boot time (0=disabled, 1=enabled) Default: -1 (use per-chip default) (int)
prefault_disable:Disable page prefaulting for pread/pwrite/reloc (default:false). For developers only. (bool)
load_detect_test:Force-enable the VGA load detect code for testing (default:false). For developers only. (bool)
force_reset_modeset_test:Force a modeset during gpu reset for testing (default:false). For developers only. (bool)
invert_brightness:Invert backlight brightness (-1 force normal, 0 machine defaults, 1 force inversion), please report PCI device ID, subsystem vendor and subsystem device ID to [email protected], if your machine needs it. It will then be included in an upcoming module version. (int)
disable_display:Disable display (default: false) (bool)
mmio_debug:Enable the MMIO debug code for the first N failures (default: off). This may negatively affect performance. (int)
verbose_state_checks:Enable verbose logs (ie. WARN_ON()) in case of unexpected hw state conditions. (bool)
nuclear_pageflip:Force enable atomic functionality on platforms that don't have full support yet. (bool)
edp_vswing:Ignore/Override vswing pre-emph table selection from VBT (0=use value from vbt [default], 1=low power swing(200mV),2=default swing(400mV)) (int)
enable_guc:Enable GuC load for GuC submission and/or HuC load. Required functionality can be selected using bitmask values. (-1=auto, 0=disable [default], 1=GuC submission, 2=HuC load) (int)
guc_log_level:GuC firmware logging level. Requires GuC to be loaded. (-1=auto [default], 0=disable, 1..4=enable with verbosity min..max) (int)
guc_firmware_path:GuC firmware path to use instead of the default one (charp)
huc_firmware_path:HuC firmware path to use instead of the default one (charp)
dmc_firmware_path:DMC firmware path to use instead of the default one (charp)
enable_dp_mst:Enable multi-stream transport (MST) for new DisplayPort sinks. (default: true) (bool)
enable_dpcd_backlight:Enable support for DPCD backlight control (default:false) (bool)
enable_gvt:Enable support for Intel GVT-g graphics virtualization host support(default:false) (bool)