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The calculation of bridge window head alignment is done by
calculate_mem_align() [*]. With the default bridge window alignment, it
is used for both head and tail alignment.
The selected head alignment does not always result in tight-fitting
resources (gap at d4f00000-d4ffffff):
d4800000-dbffffff : PCI Bus 0000:06
d4800000-d48fffff : PCI Bus 0000:07
d4800000-d4803fff : 0000:07:00.0
d4800000-d4803fff : nvme
d4900000-d49fffff : PCI Bus 0000:0a
d4900000-d490ffff : 0000:0a:00.0
d4900000-d490ffff : r8169
d4910000-d4913fff : 0000:0a:00.0
d4a00000-d4cfffff : PCI Bus 0000:0b
d4a00000-d4bfffff : 0000:0b:00.0
d4a00000-d4bfffff : 0000:0b:00.0
d4c00000-d4c07fff : 0000:0b:00.0
d4d00000-d4dfffff : PCI Bus 0000:15
d4d00000-d4d07fff : 0000:15:00.0
d4d00000-d4d07fff : xhci-hcd
d4e00000-d4efffff : PCI Bus 0000:16
d4e00000-d4e7ffff : 0000:16:00.0
d4e80000-d4e803ff : 0000:16:00.0
d4e80000-d4e803ff : ahci
d5000000-dbffffff : PCI Bus 0000:0c
This has not caused problems (for years) with the default bridge window
tail alignment that grossly over-estimates the required tail alignment
leaving more tail room than necessary. With the introduction of relaxed
tail alignment that leaves no extra tail room whatsoever, any gaps will
immediately turn into assignment failures.
Introduce head alignment calculation that ensures no gaps are left and
apply the new approach when using relaxed alignment. We may want to
consider using it for the normal alignment eventually, but as the first
step, solve only the problem with the relaxed tail alignment.
([*] I don't understand the algorithm in calculate_mem_align().)
Link: https://git.kernel.org/history/history/c/5d0a8965aea9 ("[PATCH] 2.5.14: New PCI allocation code (alpha, arm, parisc) [2/2]")
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220775
Reported-by: Malte Schröder <malte+lkml@tnxip.de>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Malte Schröder <malte+lkml@tnxip.de>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20251219174036.16738-3-ilpo.jarvinen@linux.intel.com
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. 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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 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
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