On Tue, Apr 18, 2023 at 11:31:30AM -0300, Gustavo Sousa wrote: > Quoting Rodrigo Vivi (2023-04-18 10:31:33) > > Let’s establish a merge plan for Xe, by writing down clear pre-merge goals, in > > order to avoid unnecessary delays. > > > > This initial document starts with a TODO list containing items with clear and > > measurable key results. Xe’s initial pull request should only be sent to > > dri-devel after all the items are clearly resolved. > > > > Since many of them involve some level of a community consensus, in many cases, > > the consensus will be reached in follow-up patches to this document with more > > details of the API or helpers that will be developed or modified. > > > > Besides of the items that are highlighted in this document, it is important > > to highlight that Oded, has been volunteered to give the overall ack on Xe > > driver as the way to confirm that it looks good for upstream. > > > > v2: Incorporated Daniel's feedback: > > - Do not make long-running compute a blocker. > > - Add a mention to drm-exec that that ties to vm_bind and long-running > > compute jobs. Then I also added GPUVA since I recently noticed that this > > ties also to the work Matt is doing on that front. > > - Added the devcoredump section. > > - Add the mention to Oded being volunteered for the overall ack. > > > > Cc: Dave Airlie <airlied@xxxxxxxxxx> > > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> > > Cc: Oded Gabbay <ogabbay@xxxxxxxxxx> > > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx> > > Signed-off-by: Francois Dugast <francois.dugast@xxxxxxxxx> > > Signed-off-by: Luis Strano <luis.strano@xxxxxxxxx> > > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx> > > Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx> > > Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> > > Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > > --- > > Documentation/gpu/rfc/index.rst | 4 + > > Documentation/gpu/rfc/xe.rst | 234 ++++++++++++++++++++++++++++++++ > > 2 files changed, 238 insertions(+) > > create mode 100644 Documentation/gpu/rfc/xe.rst > > > > diff --git a/Documentation/gpu/rfc/index.rst b/Documentation/gpu/rfc/index.rst > > index 476719771eef..e4f7b005138d 100644 > > --- a/Documentation/gpu/rfc/index.rst > > +++ b/Documentation/gpu/rfc/index.rst > > @@ -31,3 +31,7 @@ host such documentation: > > .. toctree:: > > > > i915_vm_bind.rst > > + > > +.. toctree:: > > + > > + xe.rst > > diff --git a/Documentation/gpu/rfc/xe.rst b/Documentation/gpu/rfc/xe.rst > > new file mode 100644 > > index 000000000000..9227a5370653 > > --- /dev/null > > +++ b/Documentation/gpu/rfc/xe.rst > > @@ -0,0 +1,234 @@ > > +========================== > > +Xe – Merge Acceptance Plan > > +========================== > > +Xe is a new driver for Intel GPUs that supports both integrated and > > +discrete platforms starting with Tiger Lake (first Intel Xe Architecture). > > + > > +This document aims to establish a merge plan for the Xe, by writing down clear > > +pre-merge goals, in order to avoid unnecessary delays. > > + > > +Xe – Overview > > +============= > > +The main motivation of Xe is to have a fresh base to work from that is > > +unencumbered by older platforms, whilst also taking the opportunity to > > +rearchitect our driver to increase sharing across the drm subsystem, both > > +leveraging and allowing us to contribute more towards other shared components > > +like TTM and drm/scheduler. > > + > > +This is also an opportunity to start from the beginning with a clean uAPI that is > > +extensible by design and already aligned with the modern userspace needs. For > > +this reason, the memory model is solely based on GPU Virtual Address space > > +bind/unbind (‘VM_BIND’) of GEM buffer objects (BOs) and execution only supporting > > +explicit synchronization. With persistent mapping across the execution, the > > +userspace does not need to provide a list of all required mappings during each > > +submission. > > + > > +The new driver leverages a lot from i915. As for display, the intent is to share > > +the display code with the i915 driver so that there is maximum reuse there. > > + > > +As for the power management area, the goal is to have a much-simplified support > > +for the system suspend states (S-states), PCI device suspend states (D-states), > > +GPU/Render suspend states (R-states) and frequency management. It should leverage > > +as much as possible all the existent PCI-subsystem infrastructure (pm and > > +runtime_pm) and underlying firmware components such PCODE and GuC for the power > > +states and frequency decisions. > > + > > +Repository: > > + > > +https://gitlab.freedesktop.org/drm/xe/kernel (branch drm-xe-next) > > + > > +Xe – Platforms > > +============== > > +Currently, Xe is already functional and has experimental support for multiple > > +platforms starting from Tiger Lake, with initial support in userspace implemented > > +in Mesa (for Iris and Anv, our OpenGL and Vulkan drivers), as well as in NEO > > +(for OpenCL and Level0). > > + > > +During a transition period, platforms will be supported by both Xe and i915. > > +However, the force_probe mechanism existent in both drivers will allow only one > > +official and by-default probe at a given time. > > + > > +For instance, in order to probe a DG2 which PCI ID is 0x5690 by Xe instead of > > +i915, the following set of parameters need to be used: > > + > > +``` > > +i915.force_probe=!5690 xe.force_probe=5690 > > +``` > > + > > +In both drivers, the ‘.require_force_probe’ protection forces the user to use the > > +force_probe parameter while the driver is under development. This protection is > > +only removed when the support for the platform and the uAPI are stable. Stability > > +which needs to be demonstrated by CI results. > > + > > +In order to avoid user space regressions, i915 will continue to support all the > > +current platforms that are already out of this protection. Xe support will be > > +forever experimental and dependent on the usage of force_probe for these > > +platforms. > > The term "these platforms" seems to be refering to the ones mentioned in the > previous sentence. Wouldn't that technically mean that Tiger Lake (which is > already out of protection) is also included into "these"? > > When we say at the beginning that "Xe is a new driver for Intel GPUs that > supports both integrated and discrete platforms starting with Tiger Lake", I was > under the impression that Tiger Lake would be the first "officially" (not > experimental) supported platform. Please notice that we are not promising any API compatibility with i915, so we are free to create a clean API aligned with the modern needs. Hence, if we removed the force_probe in i915, we cannot do the switch back to Xe otherwise we would break Linus' main rule. > > > + > > +When the time comes for Xe, the protection will be lifted on Xe and kept in i915. > > + > > +Xe driver will be protected with both STAGING Kconfig and force_probe. Changes in > > +the uAPI are expected while the driver is behind these protections. STAGING will > > +be removed when the driver uAPI gets to a mature state where we can guarantee the > > +‘no regression’ rule. Then force_probe will be lifted only for future platforms > > +that will be productized with Xe driver, but not with i915. > > + > > +Xe – Pre-Merge Goals > > +==================== > > + > > +Drm_scheduler > > +------------- > > +Xe primarily uses Firmware based scheduling (GuC FW). However, it will use > > +drm_scheduler as the scheduler ‘frontend’ for userspace submission in order to > > +resolve syncobj and dma-buf implicit sync dependencies. However, drm_scheduler is > > +not yet prepared to handle the 1-to-1 relationship between drm_gpu_scheduler and > > +drm_sched_entity. > > + > > +Deeper changes to drm_scheduler should *not* be required to get Xe accepted, but > > +some consensus needs to be reached between Xe and other community drivers that > > +could also benefit from this work, for coupling FW based/assisted submission such > > +as the ARM’s new Mali GPU driver, and others. > > + > > +As a key measurable result, the patch series introducing Xe itself shall not > > +depend on any other patch touching drm_scheduler itself that was not yet merged > > +through drm-misc. This, by itself, already includes the reach of an agreement for > > +uniform 1 to 1 relationship implementation / usage across drivers. > > + > > +GPU VA > > +------ > > +Two main goals of Xe are meeting together here: > > + > > +1) Have an uAPI that aligns with modern UMD needs. > > + > > +2) Early upstream engagement. > > + > > +RedHat engineers working on Nouveau proposed a new DRM feature to handle keeping > > +track of GPU virtual address mappings. This is still not merged upstream, but > > +this aligns very well with our goals and with our VM_BIND. The engagement with > > +upstream and the port of Xe towards GPUVA is already ongoing. > > + > > +As a key measurable result, Xe needs to be aligned with the GPU VA and working in > > +our tree. Missing Nouveau patches should *not* block Xe and any needed GPUVA > > +related patch should be independent and present on dri-devel or acked by > > +maintainers to go along with the first Xe pull request towards drm-next. > > + > > +DRM_VM_BIND > > +----------- > > +Nouveau, and Xe are all implementing ‘VM_BIND’ and new ‘Exec’ uAPIs in order to > > +fulfill the needs of the modern uAPI. Xe merge should *not* be blocked on the > > +development of a common new drm_infrastructure. However, the Xe team needs to > > +engage with the community to explore the options of a common API. > > + > > +As a key measurable result, the DRM_VM_BIND needs to be documented in this file > > +below, or this entire block deleted if the consensus is for independent drivers > > +vm_bind ioctls. > > + > > +Although having a common DRM level IOCTL for VM_BIND is not a requirement to get > > +Xe merged, it is mandatory to enforce the overall locking scheme for all major > > +structs and list (so vm and vma). So, a consensus is needed, and possibly some > > +common helpers. If helpers are needed, they should be also documented in this > > +document. > > + > > +ASYNC VM_BIND > > +------------- > > +Although having a common DRM level IOCTL for VM_BIND is not a requirement to get > > +Xe merged, it is mandatory to have a cross-driver consensus and understanding how > > +to handle async VM_BIND and interactions with userspace memory fences. Ideally > > +with helper support so people don't get it wrong in all possible ways. > > + > > +As a key measurable result, the benefits of ASYNC VM_BIND and a discussion of > > +various flavors, error handling and a sample API should be documented here or in > > +a separate document pointed to by this document. > > + > > +Userptr integration and vm_bind > > +------------------------------- > > +Different drivers implement different ways of dealing with execution of userptr. > > +With multiple drivers currently introducing support to VM_BIND, the goal is to > > +aim for a DRM consensus on what’s the best way to have that support. To some > > +extent this is already getting addressed itself with the GPUVA where likely the > > +userptr will be a GPUVA with a NULL GEM call VM bind directly on the userptr. > > +However, there are more aspects around the rules for that and the usage of > > +mmu_notifiers, locking and other aspects. > > + > > +This task here has the goal of introducing a documentation of the basic rules. > > + > > +The documentation *needs* to first live in this document (API session below) and > > +then moved to another more specific document or at Xe level or at DRM level. > > + > > +Documentation should include: > > + > > + * The userptr part of the VM_BIND api. > > + > > + * Locking, including the page-faulting case. > > + > > + * O(1) complexity under VM_BIND. > > + > > +Some parts of userptr like mmu_notifiers should become GPUVA or DRM helpers when > > +the second driver supporting VM_BIND+userptr appears. Details to be defined when > > +the time comes. > > + > > +Long running compute: minimal data structure/scaffolding > > +-------------------------------------------------------- > > +The generic scheduler code needs to include the handling of endless compute > > +contexts, with the minimal scaffolding for preempt-ctx fences (probably on the > > +drm_sched_entity) and making sure drm_scheduler can cope with the lack of job > > +completion fence. > > + > > +The goal is to achieve a consensus ahead of Xe initial pull-request, ideally with > > +this minimal drm/scheduler work, if needed, merged to drm-misc in a way that any > > +drm driver, including Xe, could re-use and add their own individual needs on top > > +in a next stage. However, this should not block the initial merge. > > + > > +This is a non-blocker item since the driver without the support for the long > > +running compute enabled is not a showstopper. > > + > > +Display integration with i915 > > +----------------------------- > > +In order to share the display code with the i915 driver so that there is maximum > > +reuse, the i915/display/ code is built twice, once for i915.ko and then for > > +xe.ko. Currently, the i915/display code in Xe tree is polluted with many 'ifdefs' > > +depending on the build target. The goal is to refactor both Xe and i915/display > > +code simultaneously in order to get a clean result before they land upstream, so > > +that display can already be part of the initial pull request towards drm-next. > > + > > +However, display code should not gate the acceptance of Xe in upstream. Xe > > +patches will be refactored in a way that display code can be removed, if needed, > > +from the first pull request of Xe towards drm-next. The expectation is that when > > +both drivers are part of the drm-tip, the introduction of cleaner patches will be > > +easier and speed up. > > + > > +Drm_exec > > +-------- > > +Helper to make dma_resv locking for a big number of buffers is getting removed in > > +the drm_exec series proposed in https://patchwork.freedesktop.org/patch/524376/ > > +If that happens, Xe needs to change and incorporate the changes in the driver. > > +The goal is to engage with the Community to understand if the best approach is to > > +move that to the drivers that are using it or if we should keep the helpers in > > +place waiting for Xe to get merged. > > + > > +This item ties into the GPUVA, VM_BIND, and even long-running compute support. > > + > > +As a key measurable result, we need to have a community consensus documented in > > +this document and the Xe driver prepared for the changes, if necessary. > > + > > +Dev_coredump > > +------------ > > + > > +Xe needs to align with other drivers on the way that the error states are > > +dumped, avoiding a Xe only error_state solution. The goal is to use devcoredump > > +infrastructure to report error states, since it produces a standardized way > > +by exposing a virtual and temporary /sys/class/devcoredump device. > > + > > +As the key measurable result, Xe driver needs to provide GPU snapshots captured > > +at hang time through devcoredump, but without depending on any core modification > > +of devcoredump infrastructure itself. > > + > > +Later, when we are in-tree, the goal is to collaborate with devcoredump > > +infrastructure with overall possible improvements, like multiple file support > > +for better organization of the dumps, snapshot support, dmesg extra print, > > +and whatever may make sense and help the overall infrastructure. > > + > > +Xe – uAPI high level overview > > +============================= > > + > > +...Warning: To be done in follow up patches after/when/where the main consensus in various items are individually reached. > > -- > > 2.39.2 > >
