Den 10.03.2019 02.31, skrev Ahmed S. Darwish: > Hello DRM/UEFI maintainers, > > Several years ago, I wrote a set of patches to dump the kernel > log to disk upon panic -- through BIOS INT 0x13 services. [1] > > The overwhelming response was that it's unsafe to do this in a > generic manner. Linus proposed a video-based viewer instead: [2] > > If you want to do the BIOS services thing, do it for video: copy the > oops to low RAM, return to real mode, re-run the graphics card POST > routines to initialize text-mode, and use the BIOS to print out the > oops. That is WAY less scary than writing to disk. > > Of course it's 2019 now though, and it's quite known that > Intel is officially obsoleting the PC/AT BIOS by 2020.. [3] > > Researching whether this can be done from UEFI, it was also clear > that UEFI "Runtime Services" do not provide any re-initialization > routines. [4] > > The maximum possible that UEFI can provide is a GOP-provided > framebuffer that's ready to use by the OS -- even after the UEFI > boot phase is marked as done through ExitBootServices(). [5] > > Of course, once native drivers like i915 or radeon take over, > such a framebuffer is toast... [6] > > Thus a possible remaining option, is to display the oops through > "minimal" DRM drivers provided for each HW variant... Since > these special drivers will run only and fully under a panic() > context though, several constraints exist: > > - The code should be fully synchronous (irqs are disabled) > - It should not allocate any dynamic memory > - It should make minimal assumptions about HW state > - It should not chain into any other kernel subsystem > - It has ample freedom to use delay-based loops and the > like, the kernel is already dead. > > How feasible is it to have such a special "DRM viewoops" > framework + its minimal drivers in the kernel? > > The target is to start from i915, since that's what in my > laptop now, and work from there.. > > Some final notes: > > - The NT kernel has a similar concept, but for storage instead. > They're used to dump core under kernel panic() situations, > and are called "Minoport storage drivers". [7] > > - Since Windows 7+, a very fancy Blue Screen of Death is > displayed, with Unicode and whatnot, implying GPU drivers > involvement. [8] > > - Mac OS X also does something similar [9] > > - On Linux laptops, the current situation is _really_ bad. > > In any graphical session, type "echo c > /proc/sysrq-trigger"; > the screen will just completely freeze... > > Desired first goal: just print the panic() log > > Thanks a lot, >
I just sent out a patchset I had lying around that tries to solve this: https://patchwork.freedesktop.org/series/57849/ Noralf. > [1] https://lore.kernel.org/lkml/20110125134748.GA10051@laptop > [2] > https://lore.kernel.org/lkml/AANLkTinU0KYiCd4p=z+=ojbkeeot2g+cayvdru02k...@mail.gmail.com > > [3] > https://uefi.org/sites/default/files/resources/Brian_Richardson_Intel_Final.pdf > > [4] UEFI v2.7 spec, Chapter 8, "Services — Runtime Services" > [5] UEFI v2.7 spec, Section 12.9, "Graphics Output Protocol" > "The Graphics Output Protocol supports this capability by > providing the EFI OS loader access to a hardware frame buffer > and enough information to allow the OS to draw directly to > the graphics output device." > > [6] linux/drivers/gpu/drm/i915/i915_drv.c::i915_kick_out_firmware_fb() > linux/drivers/gpu/drm/radeon/radeon_drv.c::radeon_pci_probe() > > [7] > https://docs.microsoft.com/en-us/windows-hardware/drivers/storage/restrictions-on-miniport-drivers-that-manage-the-boot-drive > > [8] > https://upload.wikimedia.org/wikipedia/commons/archive/5/56/20181019151937%21Bsodwindows10.png > [9] > https://upload.wikimedia.org/wikipedia/commons/4/4a/Mac_OS_X_10.2_Kernel_Panic.jpg > > --darwi > http://darwish.chasingpointers.com > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel > _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
