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The driver used a mix of virt-dma APIs and driver specific logic to process descriptors. It maintained three internal queues: ld_free, ld_queue, and ld_active as follows: - ld_free: stores the descriptors pre-allocated at probe time - ld_queue: stores descriptors after they are taken from ld_free and prepared. At the same time, vchan_tx_prep() queues them to vc->desc_allocated. The vc->desc_allocated list is then checked in rz_dmac_issue_pending() and rz_dmac_irq_handler_thread() before starting a new transfer via rz_dmac_xfer_desc(). In turn, rz_dmac_xfer_desc() grabs the next descriptor from vc->desc_issued and submits it for transfer - ld_active: stores the descriptors currently being transferred The interrupt handler moved a completed descriptor to ld_free before invoking its completion callback. Once returned to ld_free, the descriptor can be reused to prepare a new transfer. In theory, this means the descriptor could be re-prepared before its completion callback is called. Commit fully back the driver by the virt-dma APIs. With this, only ld_free need to be kept to track how many free descriptors are available. This is now done as follows: - the prepare stage removes the first descriptor from the ld_free and prepares it - the completion calls for it vc->desc_free() (rz_dmac_virt_desc_free()) which re-adds the descriptor at the end of ld_free With this, the critical areas in prepare callbacks were minimized to only getting the descriptor from the ld_free list. Introduce struct rz_dmac_chan::desc to keep track of the currently transferred descriptor. It is cleared in rz_dmac_terminate_all(), referenced from rz_dmac_issue_pending() to determine whether a new transfer can be started, and from rz_dmac_irq_handler_thread() once a descriptor has completed. Finally, the rz_dmac_device_synchronize() was updated with vchan_synchronize() call to ensure the terminated descriptor is freed and the tasklet is killed. With this, residue computation is also simplified, as it can now be handled entirely through the virt-dma APIs. The spin_lock/unlock operations from rz_dmac_irq_handler_thread() were replaced by guard as the final code after rework is simpler this way. As subsequent commits will set the Link End bit on the last descriptor of a transfer, rz_dmac_enable_hw() is also adjusted as part of the full conversion to virt-dma APIs. It no longer checks the channel enable status itself; instead, its callers verify whether the channel is enabled and whether the previous transfer has completed before starting a new one. Tested-by: John Madieu <john.madieu.xa@bp.renesas.com> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com> Tested-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com> Link: https://patch.msgid.link/20260526084710.3491480-10-claudiu.beznea@kernel.org Signed-off-by: Vinod Koul <vkoul@kernel.org> |
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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