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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-24 08:46:03 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-24 08:46:03 -0700 |
| commit | cf9610f9116d55c5a66ef9f1faecacabd93a9322 (patch) | |
| tree | 757a3d280760c654767631cab5ad8af2d86d1848 /Documentation/driver-api/generic_pt.rst | |
| download | linux-stable-cf9610f9116d55c5a66ef9f1faecacabd93a9322.tar.gz linux-stable-cf9610f9116d55c5a66ef9f1faecacabd93a9322.zip | |
Merge tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrlgrafted
Pull pin control updates from Linus Walleij:
"Core changes:
- Use the non-blocking mux_state_try_select() in the generic MUX pin
control back-end
- Free pin maps on pinctrl_generic_to_map() failure in the core
helpers
New hardware pin control:
- Qualcomm Maili TLMM SoC, PMG1110 PMIC, and Eliza LPASS LPI TLMM SoC
(this is for the low power audio, LPASS = Low Power Audio SubSystem
portions)
- Upboard support on top of the Intel pin controller
- Apple T6030 and T6031 support (just compatible strings)
- Samsung Exynos 8855 SoC
- Mediatek MT6858 SoC
- Rockchip RK3308B and RV1106 SoCs
- Airoha EN7523 and AN7563 SoCs
Improvements:
- Qualcomm TLMM GPIOs are unconditionally marked as wakeup capable
- Qualcomm improvements on top of the Qualcomm PDC (power domain
controller) irqchip improvements from tglx:s tree
- Qualcomm IPQ806x and IPQ9650 non-urgent pin grop fixups
- The NPCM8xx driver has been put into shape fixing many pin and
group definitions
- Some non-urgent Tegra 264 pin assignments are fixed up
- Some non-urgent fixups to Airoha AN7581 and AN7583 registers and
pin assignments, missing features etc"
* tag 'pinctrl-v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl: (130 commits)
dt-bindings: pinctrl: Convert TI DA850 pupd to DT schema
pinctrl: meson: sync some modify from A4
pinctrl: meson: a4: Add input enable pin configuration
pinctrl: realtek: rtd1625: remove unused group name spdif_sel
pinctrl: realtek: rtd1625: fix base_bit for VE4 GPIO 13
dt-bindings: pinctrl: microchip,pic32mzda-pinctrl: Convert to DT schema
Revert "Merge branch 'ib-rsk7204' into devel"
pinctrl: rockchip: Add RV1106 pinctrl support
dt-bindings: pinctrl: rockchip: Add RV1106 compatible
pinctrl: rockchip: Decode drive strength in the get function
pinctrl: fix PINCTRL_GENERIC_MUX not always being selectable
pinctrl: airoha: add support of an7563 SoC
dt-bindings: pinctrl: airoha: add support of an7563 pin controller
pinctrl: airoha: try to find chip scu node by phandle first
pinctrl: airoha: add support of en7523 SoC
dt-bindings: pinctrl: airoha: add support of en7523 pin controller
pinctrl: airoha: an7583: add support for olt pinmux
pinctrl: airoha: an7583: add support for pon_alt pinmux
pinctrl: airoha: an7583: add support for npu_uart pinmux
dt-bindings: pinctrl: airoha: an7583: add missed features
...
Diffstat (limited to 'Documentation/driver-api/generic_pt.rst')
| -rw-r--r-- | Documentation/driver-api/generic_pt.rst | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/Documentation/driver-api/generic_pt.rst b/Documentation/driver-api/generic_pt.rst new file mode 100644 index 000000000..fd29d1b52 --- /dev/null +++ b/Documentation/driver-api/generic_pt.rst @@ -0,0 +1,137 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================== +Generic Radix Page Table +======================== + +.. kernel-doc:: include/linux/generic_pt/common.h + :doc: Generic Radix Page Table + +.. kernel-doc:: drivers/iommu/generic_pt/pt_defs.h + :doc: Generic Page Table Language + +Usage +===== + +Generic PT is structured as a multi-compilation system. Since each format +provides an API using a common set of names there can be only one format active +within a compilation unit. This design avoids function pointers around the low +level API. + +Instead the function pointers can end up at the higher level API (i.e. +map/unmap, etc.) and the per-format code can be directly inlined into the +per-format compilation unit. For something like IOMMU each format will be +compiled into a per-format IOMMU operations kernel module. + +For this to work the .c file for each compilation unit will include both the +format headers and the generic code for the implementation. For instance in an +implementation compilation unit the headers would normally be included as +follows: + +generic_pt/fmt/iommu_amdv1.c:: + + #include <linux/generic_pt/common.h> + #include "defs_amdv1.h" + #include "../pt_defs.h" + #include "amdv1.h" + #include "../pt_common.h" + #include "../pt_iter.h" + #include "../iommu_pt.h" /* The IOMMU implementation */ + +iommu_pt.h includes definitions that will generate the operations functions for +map/unmap/etc. using the definitions provided by AMDv1. The resulting module +will have exported symbols named like pt_iommu_amdv1_init(). + +Refer to drivers/iommu/generic_pt/fmt/iommu_template.h for an example of how the +IOMMU implementation uses multi-compilation to generate per-format ops structs +pointers. + +The format code is written so that the common names arise from #defines to +distinct format specific names. This is intended to aid debuggability by +avoiding symbol clashes across all the different formats. + +Exported symbols and other global names are mangled using a per-format string +via the NS() helper macro. + +The format uses struct pt_common as the top-level struct for the table, +and each format will have its own struct pt_xxx which embeds it to store +format-specific information. + +The implementation will further wrap struct pt_common in its own top-level +struct, such as struct pt_iommu_amdv1. + +Format functions at the struct pt_common level +---------------------------------------------- + +.. kernel-doc:: include/linux/generic_pt/common.h + :identifiers: +.. kernel-doc:: drivers/iommu/generic_pt/pt_common.h + +Iteration Helpers +----------------- + +.. kernel-doc:: drivers/iommu/generic_pt/pt_iter.h + +Writing a Format +---------------- + +It is best to start from a simple format that is similar to the target. x86_64 +is usually a good reference for something simple, and AMDv1 is something fairly +complete. + +The required inline functions need to be implemented in the format header. +These should all follow the standard pattern of:: + + static inline pt_oaddr_t amdv1pt_entry_oa(const struct pt_state *pts) + { + [..] + } + #define pt_entry_oa amdv1pt_entry_oa + +where a uniquely named per-format inline function provides the implementation +and a define maps it to the generic name. This is intended to make debug symbols +work better. inline functions should always be used as the prototypes in +pt_common.h will cause the compiler to validate the function signature to +prevent errors. + +Review pt_fmt_defaults.h to understand some of the optional inlines. + +Once the format compiles then it should be run through the generic page table +kunit test in kunit_generic_pt.h using kunit. For example:: + + $ tools/testing/kunit/kunit.py run --build_dir build_kunit_x86_64 --arch x86_64 --kunitconfig ./drivers/iommu/generic_pt/.kunitconfig amdv1_fmt_test.* + [...] + [11:15:08] Testing complete. Ran 9 tests: passed: 9 + [11:15:09] Elapsed time: 3.137s total, 0.001s configuring, 2.368s building, 0.311s running + +The generic tests are intended to prove out the format functions and give +clearer failures to speed up finding the problems. Once those pass then the +entire kunit suite should be run. + +IOMMU Invalidation Features +--------------------------- + +Invalidation is how the page table algorithms synchronize with a HW cache of the +page table memory, typically called the TLB (or IOTLB for IOMMU cases). + +The TLB can store present PTEs, non-present PTEs and table pointers, depending +on its design. Every HW has its own approach on how to describe what has changed +to have changed items removed from the TLB. + +PT_FEAT_FLUSH_RANGE +~~~~~~~~~~~~~~~~~~~ + +PT_FEAT_FLUSH_RANGE is the easiest scheme to understand. It tries to generate a +single range invalidation for each operation, over-invalidating if there are +gaps of VA that don't need invalidation. This trades off impacted VA for number +of invalidation operations. It does not keep track of what is being invalidated; +however, if pages have to be freed then page table pointers have to be cleaned +from the walk cache. The range can start/end at any page boundary. + +PT_FEAT_FLUSH_RANGE_NO_GAPS +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +PT_FEAT_FLUSH_RANGE_NO_GAPS is similar to PT_FEAT_FLUSH_RANGE; however, it tries +to minimize the amount of impacted VA by issuing extra flush operations. This is +useful if the cost of processing VA is very high, for instance because a +hypervisor is processing the page table with a shadowing algorithm. |
