Edited by radcliff_17 at 2019-3-10 13:46

Because of the firmware issue, the bootline must be tweak twice at boot time. + Grub is not recording the change. + quiet splash becomes splash quiet=abnormal splash screen=Grub is not recording the first tweak=Deepin issue. All distros that support secure boot are recording it.
1. In Ubiquity on startup
2. On first restart
3. Edit Grub
-Ubiquity & First Restart
Replace quiet splash by iommu=soft + crtl+x to Save & Exit
Installer bootline modification in <> terminal or from Windows with NotePad++ (grub.cfg):

1. linux        /live/vmlinuz.efi boot=live union=overlay livecd-installer locale=zh_CN iommu=soft --

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-Editing Grub to boot normally (dual boot or not):

1. sudo -i deepin-editor /etc/default/grub
   
2. # Written by com.deepin.daemon.Grub2
   
3. DEEPIN_GFXMODE_DETECT=2
   
4. GRUB_CMDLINE_LINUX="iommu=soft"
   
5. GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
   
6. GRUB_DEFAULT=0
   
7. GRUB_DISTRIBUTOR="`/usr/bin/lsb_release -d -s 2>/dev/null || echo Deepin`"
   
8. GRUB_GFXMODE=1920x1080,1680x1050,1280x1024,1440x900,1280x800,1280x720,1024x768,auto
   
9. GRUB_THEME=/boot/grub/themes/deepin-fallback/theme.txt
   
10. GRUB_TIMEOUT=5

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-Final result:

1. [font=Tahoma][size=3]cat /proc/cmdline
   
2. BOOT_IMAGE=/boot/vmlinuz-5.0.0-050000-generic root=UUID=8f5a58a8-7957-4246-8204-ef2b7d73100e ro iommu=soft quiet splash DEEPIN_GFXMODE=[/size][/font]

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1. mokutil  --sb-state
   
2. SecureBoot enabled

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Until AMD's provides a BIOS correction, we must do this modification to run Deepin. Lastly, 15.9 is not by any means unstable here, it runs like a Swiss clock.