Hi all,

I must have omitted a few pieces of information in fact :
  - The description of the bug
  - Error messages
  - The text files (logs, ...) I mentioned in my previous post

The files are joined as an attachement to this post, and here follow my bug description and error messages extracts.

With Linux 4.5.x or below all is good :
  - Screen resolution of 1600x900 (native screen resolution)
  - Accelerated 3D graphics on AMD TURKS hardware
  - Plymouth shows up and animates well both on OS startup and OS shutdown
  - No scary message in kernel logs (dmesg)

With Linux 4.6.x or above all is bad :
  - Screen resolution of 1152x864 (lower than native)
  - Software rendered 3D graphics on llvmpipe
  - Plymouth neither shows up on OS startup nor on OS shutdown
  - Scary messages in kernel logs (extracts follow) :


[    5.291603] [drm] Initialized drm 1.1.0 20060810
...
[    5.353156] [drm] radeon kernel modesetting enabled.
[    5.353216] call_modprobe: symbol:kgd2kfd_init   2 
[    5.359409] CRAT table not found
[    5.359410] Finished initializing topology ret=0
[    5.359425] kfd kfd: Initialized module
[    5.359614] checking generic (b0000000 3cc000) vs hw (b0000000 10000000)
[    5.359615] fb: switching to radeondrmfb from simple
[    5.359644] Console: switching to colour dummy device 80x25
[    5.359926] [drm] initializing kernel modesetting (TURKS 0x1002:0x6840 0x1179:0xFB41 0x00).
[    5.359936] [drm] register mmio base: 0xC2000000
[    5.359937] [drm] register mmio size: 131072
[    5.359957] ------------[ cut here ]------------
[    5.359961] WARNING: CPU: 0 PID: 116 at /build/linux-akdJXO/linux-4.8.0/arch/x86/mm/ioremap.c:121 __ioremap_caller+0x1ec/0x370
[    5.359962] ioremap on RAM at 0x0000000000000000 - 0x000000000001ffff
[    5.359963] Modules linked in: amdkfd radeon(+) r8169 mii i2c_algo_bit ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ahci(+) libahci drm wmi ehci_pci xhci_pci fjes ehci_hcd video thermal xhci_hcd usbcore usb_common button
[    5.359978] CPU: 0 PID: 116 Comm: systemd-udevd Not tainted 4.8.0-16-generic #17-Ubuntu
[    5.359978] Hardware name: TOSHIBA SATELLITE L875-10G/Type2 - Board Product Name1, BIOS 6.50 3/25/2013
[    5.359980]  0000000000000286 000000001712e9ce ffffffffbe973f14 ffff8b3f3cebf8c0
[    5.359982]  0000000000000000 ffffffffbe67f93e 0000000000000000 ffff8b3f3cebf918
[    5.359985]  ffffffffbe9cf198 0000000000020000 0000000000000002 0000000000000000
[    5.359987] Call Trace:
[    5.359992]  [<ffffffffbe973f14>] ? dump_stack+0x5c/0x78
[    5.359995]  [<ffffffffbe67f93e>] ? __warn+0xbe/0xe0
[    5.359997]  [<ffffffffbe9cf198>] ? pci_map_rom+0x58/0xd0
[    5.359999]  [<ffffffffbe67f9bf>] ? warn_slowpath_fmt+0x5f/0x80
[    5.360040]  [<ffffffffc0536877>] ? igp_read_bios_from_vram+0x57/0xa0 [radeon]
[    5.360042]  [<ffffffffbe66905c>] ? __ioremap_caller+0x1ec/0x370
[    5.360044]  [<ffffffffbe9cf198>] ? pci_map_rom+0x58/0xd0
[    5.360075]  [<ffffffffc05368f5>] ? radeon_read_bios.isra.2+0x35/0xc0 [radeon]
[    5.360102]  [<ffffffffc0536c0c>] ? radeon_get_bios+0x28c/0xfc0 [radeon]
[    5.360105]  [<ffffffffbe6d74ca>] ? vprintk_emit+0x35a/0x520
[    5.360108]  [<ffffffffbe7f1f0d>] ? kmem_cache_alloc_trace+0x18d/0x1d0
[    5.360145]  [<ffffffffc057410f>] ? evergreen_init+0xf/0x390 [radeon]
[    5.360173]  [<ffffffffc0502e2e>] ? radeon_device_init+0x87e/0xcb0 [radeon]
[    5.360198]  [<ffffffffc05056a5>] ? radeon_driver_load_kms+0x95/0x210 [radeon]
[    5.360217]  [<ffffffffc041326c>] ? drm_dev_register+0x9c/0xc0 [drm]
[    5.360230]  [<ffffffffc0415238>] ? drm_get_pci_dev+0x88/0x1d0 [drm]
[    5.360232]  [<ffffffffbe9cb72f>] ? local_pci_probe+0x3f/0x90
[    5.360234]  [<ffffffffbe9ccb09>] ? pci_device_probe+0x109/0x160
[    5.360237]  [<ffffffffbeac956a>] ? driver_probe_device+0x21a/0x420
[    5.360240]  [<ffffffffbeac984a>] ? __driver_attach+0xda/0xe0
[    5.360242]  [<ffffffffbeac9770>] ? driver_probe_device+0x420/0x420
[    5.360244]  [<ffffffffbeac7087>] ? bus_for_each_dev+0x67/0xb0
[    5.360246]  [<ffffffffbeac873a>] ? bus_add_driver+0x16a/0x260
[    5.360248]  [<ffffffffc066f000>] ? 0xffffffffc066f000
[    5.360249]  [<ffffffffbeaca1a7>] ? driver_register+0x57/0xc0
[    5.360251]  [<ffffffffc066f000>] ? 0xffffffffc066f000
[    5.360253]  [<ffffffffbe60218b>] ? do_one_initcall+0x4b/0x190
[    5.360255]  [<ffffffffbe7f1ed0>] ? kmem_cache_alloc_trace+0x150/0x1d0
[    5.360258]  [<ffffffffbe7887bc>] ? do_init_module+0x5b/0x1ed
[    5.360261]  [<ffffffffbe70ba58>] ? load_module+0x1938/0x1ca0
[    5.360262]  [<ffffffffbe707c00>] ? m_show+0x1b0/0x1b0
[    5.360265]  [<ffffffffbe70c006>] ? SYSC_finit_module+0xc6/0xf0
[    5.360268]  [<ffffffffbecfbfb6>] ? entry_SYSCALL_64_fastpath+0x1e/0xa8
[    5.360270] ---[ end trace a3dcc2b343f5d80b ]---
[    5.360304] [drm:radeon_get_bios [radeon]] *ERROR* Unable to locate a BIOS ROM
[    5.360309] radeon 0000:01:00.0: Fatal error during GPU init
[    5.360312] [drm] radeon: finishing device.
[    5.360313] [TTM] Memory type 2 has not been initialized
[    5.361148] scsi host0: ahci
[    5.367568] radeon: probe of 0000:01:00.0 failed with error -22

I havent got a peanut about what is happenging since Linux 4.6.0 ; any idea ?

I have tried to attempt a bissection, but got the timeline messed up, so I will rety in the following days ...

Sincerely,
Vécu