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Diffstat (limited to 'Documentation/gpu/todo.rst')
| -rw-r--r-- | Documentation/gpu/todo.rst | 250 |
1 files changed, 169 insertions, 81 deletions
diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst index 60d1d7ee0719..393d218e4a0c 100644 --- a/Documentation/gpu/todo.rst +++ b/Documentation/gpu/todo.rst @@ -222,7 +222,7 @@ Convert drivers to use drm_fbdev_generic_setup() Most drivers can use drm_fbdev_generic_setup(). Driver have to implement atomic modesetting and GEM vmap support. Historically, generic fbdev emulation expected the framebuffer in system memory or system-like memory. By employing -struct dma_buf_map, drivers with frambuffers in I/O memory can be supported +struct iosys_map, drivers with frambuffers in I/O memory can be supported as well. Contact: Maintainer of the driver you plan to convert @@ -234,13 +234,35 @@ Reimplement functions in drm_fbdev_fb_ops without fbdev A number of callback functions in drm_fbdev_fb_ops could benefit from being rewritten without dependencies on the fbdev module. Some of the -helpers could further benefit from using struct dma_buf_map instead of +helpers could further benefit from using struct iosys_map instead of raw pointers. Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter Level: Advanced +Benchmark and optimize blitting and format-conversion function +-------------------------------------------------------------- + +Drawing to dispay memory quickly is crucial for many applications' +performance. + +On at least x86-64, sys_imageblit() is significantly slower than +cfb_imageblit(), even though both use the same blitting algorithm and +the latter is written for I/O memory. It turns out that cfb_imageblit() +uses movl instructions, while sys_imageblit apparently does not. This +seems to be a problem with gcc's optimizer. DRM's format-conversion +helpers might be subject to similar issues. + +Benchmark and optimize fbdev's sys_() helpers and DRM's format-conversion +helpers. In cases that can be further optimized, maybe implement a different +algorithm. For micro-optimizations, use movl/movq instructions explicitly. +That might possibly require architecture-specific helpers (e.g., storel() +storeq()). + +Contact: Thomas Zimmermann <tzimmermann@suse.de> + +Level: Intermediate drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup ----------------------------------------------------------------- @@ -268,17 +290,6 @@ Contact: Daniel Vetter Level: Intermediate -Clean up mmap forwarding ------------------------- - -A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. -And also a lot of them forward dma-buf mmap to the gem mmap implementations. -There's drm_gem_prime_mmap() for this now, but still needs to be rolled out. - -Contact: Daniel Vetter - -Level: Intermediate - Generic fbdev defio support --------------------------- @@ -311,42 +322,6 @@ Contact: Daniel Vetter, Noralf Tronnes Level: Advanced -Garbage collect fbdev scrolling acceleration --------------------------------------------- - -Scroll acceleration has been disabled in fbcon. Now it works as the old -SCROLL_REDRAW mode. A ton of code was removed in fbcon.c and the hook bmove was -removed from fbcon_ops. -Remaining tasks: - -- a bunch of the hooks in fbcon_ops could be removed or simplified by calling - directly instead of the function table (with a switch on p->rotate) - -- fb_copyarea is unused after this, and can be deleted from all drivers - -- after that, fb_copyarea can be deleted from fb_ops in include/linux/fb.h as - well as cfb_copyarea - -Note that not all acceleration code can be deleted, since clearing and cursor -support is still accelerated, which might be good candidates for further -deletion projects. - -Contact: Daniel Vetter - -Level: Intermediate - -idr_init_base() ---------------- - -DRM core&drivers uses a lot of idr (integer lookup directories) for mapping -userspace IDs to internal objects, and in most places ID=0 means NULL and hence -is never used. Switching to idr_init_base() for these would make the idr more -efficient. - -Contact: Daniel Vetter - -Level: Starter - struct drm_gem_object_funcs --------------------------- @@ -356,19 +331,6 @@ converted, except for struct drm_driver.gem_prime_mmap. Level: Intermediate -Rename CMA helpers to DMA helpers ---------------------------------- - -CMA (standing for contiguous memory allocator) is really a bit an accident of -what these were used for first, a much better name would be DMA helpers. In the -text these should even be called coherent DMA memory helpers (so maybe CDM, but -no one knows what that means) since underneath they just use dma_alloc_coherent. - -Contact: Laurent Pinchart, Daniel Vetter - -Level: Intermediate (mostly because it is a huge tasks without good partial -milestones, not technically itself that challenging) - connector register/unregister fixes ----------------------------------- @@ -445,24 +407,54 @@ Contact: Emil Velikov, respective driver maintainers Level: Intermediate -Use struct dma_buf_map throughout codebase ------------------------------------------- +Use struct iosys_map throughout codebase +---------------------------------------- -Pointers to shared device memory are stored in struct dma_buf_map. Each +Pointers to shared device memory are stored in struct iosys_map. Each instance knows whether it refers to system or I/O memory. Most of the DRM-wide -interface have been converted to use struct dma_buf_map, but implementations +interface have been converted to use struct iosys_map, but implementations often still use raw pointers. -The task is to use struct dma_buf_map where it makes sense. +The task is to use struct iosys_map where it makes sense. -* Memory managers should use struct dma_buf_map for dma-buf-imported buffers. -* TTM might benefit from using struct dma_buf_map internally. -* Framebuffer copying and blitting helpers should operate on struct dma_buf_map. +* Memory managers should use struct iosys_map for dma-buf-imported buffers. +* TTM might benefit from using struct iosys_map internally. +* Framebuffer copying and blitting helpers should operate on struct iosys_map. Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian König, Daniel Vetter Level: Intermediate +Review all drivers for setting struct drm_mode_config.{max_width,max_height} correctly +-------------------------------------------------------------------------------------- + +The values in struct drm_mode_config.{max_width,max_height} describe the +maximum supported framebuffer size. It's the virtual screen size, but many +drivers treat it like limitations of the physical resolution. + +The maximum width depends on the hardware's maximum scanline pitch. The +maximum height depends on the amount of addressable video memory. Review all +drivers to initialize the fields to the correct values. + +Contact: Thomas Zimmermann <tzimmermann@suse.de> + +Level: Intermediate + +Request memory regions in all drivers +------------------------------------- + +Go through all drivers and add code to request the memory regions that the +driver uses. This requires adding calls to request_mem_region(), +pci_request_region() or similar functions. Use helpers for managed cleanup +where possible. + +Drivers are pretty bad at doing this and there used to be conflicts among +DRM and fbdev drivers. Still, it's the correct thing to do. + +Contact: Thomas Zimmermann <tzimmermann@suse.de> + +Level: Starter + Core refactorings ================= @@ -480,8 +472,12 @@ This is a really varied tasks with lots of little bits and pieces: achieved by using an IPI to the local processor. * There's a massive confusion of different panic handlers. DRM fbdev emulation - helpers have one, but on top of that the fbcon code itself also has one. We - need to make sure that they stop fighting over each another. + helpers had their own (long removed), but on top of that the fbcon code itself + also has one. We need to make sure that they stop fighting over each other. + This is worked around by checking ``oops_in_progress`` at various entry points + into the DRM fbdev emulation helpers. A much cleaner approach here would be to + switch fbcon to the `threaded printk support + <https://lwn.net/Articles/800946/>`_. * ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and isn't a full solution for panic paths. We need to make sure that it only @@ -493,16 +489,15 @@ This is a really varied tasks with lots of little bits and pieces: even spinlocks (because NMI and hardirq can panic too). We need to either make sure to not call such paths, or trylock everything. Really tricky. -* For the above locking troubles reasons it's pretty much impossible to - attempt a synchronous modeset from panic handlers. The only thing we could - try to achive is an atomic ``set_base`` of the primary plane, and hope that - it shows up. Everything else probably needs to be delayed to some worker or - something else which happens later on. Otherwise it just kills the box - harder, prevent the panic from going out on e.g. netconsole. +* A clean solution would be an entirely separate panic output support in KMS, + bypassing the current fbcon support. See `[PATCH v2 0/3] drm: Add panic handling + <https://lore.kernel.org/dri-devel/20190311174218.51899-1-noralf@tronnes.org/>`_. -* There's also proposal for a simplied DRM console instead of the full-blown - fbcon and DRM fbdev emulation. Any kind of panic handling tricks should - obviously work for both console, in case we ever get kmslog merged. +* Encoding the actual oops and preceding dmesg in a QR might help with the + dread "important stuff scrolled away" problem. See `[RFC][PATCH] Oops messages + transfer using QR codes + <https://lore.kernel.org/lkml/1446217392-11981-1-git-send-email-alexandru.murtaza@intel.com/>`_ + for some example code that could be reused. Contact: Daniel Vetter @@ -583,6 +578,20 @@ Level: Advanced Better Testing ============== +Add unit tests using the Kernel Unit Testing (KUnit) framework +-------------------------------------------------------------- + +The `KUnit <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_ +provides a common framework for unit tests within the Linux kernel. Having a +test suite would allow to identify regressions earlier. + +A good candidate for the first unit tests are the format-conversion helpers in +``drm_format_helper.c``. + +Contact: Javier Martinez Canillas <javierm@redhat.com> + +Level: Intermediate + Enable trinity for DRM ---------------------- @@ -642,6 +651,17 @@ See drivers/gpu/drm/amd/display/TODO for tasks. Contact: Harry Wentland, Alex Deucher +vmwgfx: Replace hashtable with Linux' implementation +---------------------------------------------------- + +The vmwgfx driver uses its own hashtable implementation. Replace the +code with Linux' implementation and update the callers. It's mostly a +refactoring task, but the interfaces are different. + +Contact: Zack Rusin, Thomas Zimmermann <tzimmermann@suse.de> + +Level: Intermediate + Bootsplash ========== @@ -659,6 +679,74 @@ Contact: Sam Ravnborg Level: Advanced +Brightness handling on devices with multiple internal panels +============================================================ + +On x86/ACPI devices there can be multiple backlight firmware interfaces: +(ACPI) video, vendor specific and others. As well as direct/native (PWM) +register programming by the KMS driver. + +To deal with this backlight drivers used on x86/ACPI call +acpi_video_get_backlight_type() which has heuristics (+quirks) to select +which backlight interface to use; and backlight drivers which do not match +the returned type will not register themselves, so that only one backlight +device gets registered (in a single GPU setup, see below). + +At the moment this more or less assumes that there will only +be 1 (internal) panel on a system. + +On systems with 2 panels this may be a problem, depending on +what interface acpi_video_get_backlight_type() selects: + +1. native: in this case the KMS driver is expected to know which backlight + device belongs to which output so everything should just work. +2. video: this does support controlling multiple backlights, but some work + will need to be done to get the output <-> backlight device mapping + +The above assumes both panels will require the same backlight interface type. +Things will break on systems with multiple panels where the 2 panels need +a different type of control. E.g. one panel needs ACPI video backlight control, +where as the other is using native backlight control. Currently in this case +only one of the 2 required backlight devices will get registered, based on +the acpi_video_get_backlight_type() return value. + +If this (theoretical) case ever shows up, then supporting this will need some +work. A possible solution here would be to pass a device and connector-name +to acpi_video_get_backlight_type() so that it can deal with this. + +Note in a way we already have a case where userspace sees 2 panels, +in dual GPU laptop setups with a mux. On those systems we may see +either 2 native backlight devices; or 2 native backlight devices. + +Userspace already has code to deal with this by detecting if the related +panel is active (iow which way the mux between the GPU and the panels +points) and then uses that backlight device. Userspace here very much +assumes a single panel though. It picks only 1 of the 2 backlight devices +and then only uses that one. + +Note that all userspace code (that I know off) is currently hardcoded +to assume a single panel. + +Before the recent changes to not register multiple (e.g. video + native) +/sys/class/backlight devices for a single panel (on a single GPU laptop), +userspace would see multiple backlight devices all controlling the same +backlight. + +To deal with this userspace had to always picks one preferred device under +/sys/class/backlight and will ignore the others. So to support brightness +control on multiple panels userspace will need to be updated too. + +There are plans to allow brightness control through the KMS API by adding +a "display brightness" property to drm_connector objects for panels. This +solves a number of issues with the /sys/class/backlight API, including not +being able to map a sysfs backlight device to a specific connector. Any +userspace changes to add support for brightness control on devices with +multiple panels really should build on top of this new KMS property. + +Contact: Hans de Goede + +Level: Advanced + Outside DRM =========== |