759aaa10c7
Add reset hook for sdm845 based platforms to turn off the wait-for-safe sequence. Understanding how wait-for-safe logic affects USB and UFS performance on MTP845 and DB845 boards: Qcom's implementation of arm,mmu-500 adds a WAIT-FOR-SAFE logic to address under-performance issues in real-time clients, such as Display, and Camera. On receiving an invalidation requests, the SMMU forwards SAFE request to these clients and waits for SAFE ack signal from real-time clients. The SAFE signal from such clients is used to qualify the start of invalidation. This logic is controlled by chicken bits, one for each - MDP (display), IFE0, and IFE1 (camera), that can be accessed only from secure software on sdm845. This configuration, however, degrades the performance of non-real time clients, such as USB, and UFS etc. This happens because, with wait-for-safe logic enabled the hardware tries to throttle non-real time clients while waiting for SAFE ack signals from real-time clients. On mtp845 and db845 devices, with wait-for-safe logic enabled by the bootloaders we see degraded performance of USB and UFS when kernel enables the smmu stage-1 translations for these clients. Turn off this wait-for-safe logic from the kernel gets us back the perf of USB and UFS devices until we re-visit this when we start seeing perf issues on display/camera on upstream supported SDM845 platforms. The bootloaders on these boards implement secure monitor callbacks to handle a specific command - QCOM_SCM_SVC_SMMU_PROGRAM with which the logic can be toggled. There are other boards such as cheza whose bootloaders don't enable this logic. Such boards don't implement callbacks to handle the specific SCM call so disabling this logic for such boards will be a no-op. This change is inspired by the downstream change from Patrick Daly to address performance issues with display and camera by handling this wait-for-safe within separte io-pagetable ops to do TLB maintenance. So a big thanks to him for the change and for all the offline discussions. Without this change the UFS reads are pretty slow: $ time dd if=/dev/sda of=/dev/zero bs=1048576 count=10 conv=sync 10+0 records in 10+0 records out 10485760 bytes (10.0MB) copied, 22.394903 seconds, 457.2KB/s real 0m 22.39s user 0m 0.00s sys 0m 0.01s With this change they are back to rock! $ time dd if=/dev/sda of=/dev/zero bs=1048576 count=300 conv=sync 300+0 records in 300+0 records out 314572800 bytes (300.0MB) copied, 1.030541 seconds, 291.1MB/s real 0m 1.03s user 0m 0.00s sys 0m 0.54s Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org> Reviewed-by: Robin Murphy <robin.murphy@arm.com> Reviewed-by: Stephen Boyd <swboyd@chromium.org> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org> Signed-off-by: Will Deacon <will@kernel.org> |
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| fs | ||
| include | ||
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| ipc | ||
| kernel | ||
| lib | ||
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| samples | ||
| scripts | ||
| security | ||
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| usr | ||
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| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
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| .gitignore | ||
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| README | ||
README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.