On Mon, Mar 11, 2019 at 11:04:19AM +0200, Jani Nikula wrote: > On Sun, 10 Mar 2019, "Ahmed S. Darwish" <darwish...@gmail.com> wrote: > > 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? > > Please first better define what you want to achieve. > > Do you want to store the dmesg or oops (like your original series > suggests) or do you want to display the oops? Do you want the facility > to be functioning at all times, or only when specifically requested in > advance by the user? If you want to display the oops, do you want it to > also work when the display is disabled at the time of the oops? What if > the display is at attached to a port on a dock? > > There's at least kdump, ramoops, and netconsole that can be used to > achieve some of what you want. How do they fall short for you?
Assuming the use-case is to get an oops to display on a kms driver, we do have a fairly comprehensive plan of what that's should look like: https://dri.freedesktop.org/docs/drm/gpu/todo.html#make-panic-handling-work This takes into account all the failed previous attempts at trying to get an oops to display. It's conceptually a match with your viewoops framework I think. -Daniel > > BR, > Jani. > > > > > > 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, > > > > [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 > > -- > Jani Nikula, Intel Open Source Graphics Center -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
