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While drm_gem_shmem_object does most of the job we need it to do, the way sub-resources (pages, sgt, vmap) are handled and their lifetimes gets in the way of BO reclaim. There has been attempts to address that [1], but in the meantime, new gem_shmem users were introduced (accel drivers), and some of them manually free some of these resources. This makes things harder to control/sanitize/validate. Thomas Zimmerman is not a huge fan of enforcing lifetimes of sub-resources and forcing gem_shmem users to go through new gem_shmem helpers when they need manual control of some sort, and I believe this is a dead end if we don't force users to follow some stricter rules through carefully designed helpers, because there will always be one user doing crazy things with gem_shmem_object internals, which ends up tripping out the common helpers when they are called. The consensus we reached was that we would be better off forking gem_shmem in panthor. So here we are, parting ways with gem_shmem. The current transition tries to minimize the changes, but there are still some aspects that are different, the main one being that we no longer have a pages_use_count, and pages stays around until the GEM object is destroyed (or when evicted once we've added a shrinker). The sgt also no longer retains pages. This is losely based on how msm does things by the way. If there's any interest in sharing code (probably with msm, since the panthor shrinker is going to be losely based on the msm implementation), we can always change gears and do that once we have everything working/merged. [1]https://patchwork.kernel.org/project/dri-devel/patch/20240105184624.508603-1-dmitry.osipenko@collabora.com/ v2: - Fix refcounting - Add a _locked suffix to a bunch of functions expecting the resv lock to be held - Take the lock before releasing resources in panthor_gem_free_object() v3: - Use ERR_CAST() to fix an ERR-ptr deref - Add missing resv_[un]lock() around a panthor_gem_backing_unpin_locked() call v4: - Fix an error path in panthor_gem_vmap_get_locked() - Don't leave bo->base.pages with an ERR_PTR() - Make panthor_gem_{pin,unpin}[_locked]() more consistent - Don't fail in panthor_gem_dev_map_get_sgt_locked() if the pages are not allocated v5: - Add missing static specifier on our vm_ops v6: - Fix huge_fault handling - s/uint32_t/u32/ - s/drm_dbg_kms/drm_dbg_driver/ - Collect R-bs v7: - No changes Reviewed-by: Steven Price <steven.price@arm.com> Reviewed-by: Liviu Dudau <liviu.dudau@arm.com> Link: https://patch.msgid.link/20260401134854.2275433-7-boris.brezillon@collabora.com Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com> |
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Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst