mirror of https://gitee.com/openkylin/linux.git
12885ecbfe
This introduces support for CRC readback on gf119+, using the documentation generously provided to us by Nvidia: https://github.com/NVIDIA/open-gpu-doc/blob/master/Display-CRC/display-crc.txt We expose all available CRC sources. SF, SOR, PIOR, and DAC are exposed through a single set of "outp" sources: outp-active/auto for a CRC of the scanout region, outp-complete for a CRC of both the scanout and blanking/sync region combined, and outp-inactive for a CRC of only the blanking/sync region. For each source, nouveau selects the appropriate tap point based on the output path in use. We also expose an "rg" source, which allows for capturing CRCs of the scanout raster before it's encoded into a video signal in the output path. This tap point is referred to as the raster generator. Note that while there's some other neat features that can be used with CRC capture on nvidia hardware, like capturing from two CRC sources simultaneously, I couldn't see any usecase for them and did not implement them. Nvidia only allows for accessing CRCs through a shared DMA region that we program through the core EVO/NvDisplay channel which is referred to as the notifier context. The notifier context is limited to either 255 (for Fermi-Pascal) or 2047 (Volta+) entries to store CRCs in, and unfortunately the hardware simply drops CRCs and reports an overflow once all available entries in the notifier context are filled. Since the DRM CRC API and igt-gpu-tools don't expect there to be a limit on how many CRCs can be captured, we work around this in nouveau by allocating two separate notifier contexts for each head instead of one. We schedule a vblank worker ahead of time so that once we start getting close to filling up all of the available entries in the notifier context, we can swap the currently used notifier context out with another pre-prepared notifier context in a manner similar to page flipping. Unfortunately, the hardware only allows us to this by flushing two separate updates on the core channel: one to release the current notifier context handle, and one to program the next notifier context's handle. When the hardware processes the first update, the CRC for the current frame is lost. However, the second update can be flushed immediately without waiting for the first to complete so that CRC generation resumes on the next frame. According to Nvidia's hardware engineers, there isn't any cleaner way of flipping notifier contexts that would avoid this. Since using vblank workers to swap out the notifier context will ensure we can usually flush both updates to hardware within the timespan of a single frame, we can also ensure that there will only be exactly one frame lost between the first and second update being executed by the hardware. This gives us the guarantee that we're always correctly matching each CRC entry with it's respective frame even after a context flip. And since IGT will retrieve the CRC entry for a frame by waiting until it receives a CRC for any subsequent frames, this doesn't cause an issue with any tests and is much simpler than trying to change the current DRM API to accommodate. In order to facilitate testing of correct handling of this limitation, we also expose a debugfs interface to manually control the threshold for when we start trying to flip the notifier context. We will use this in igt to trigger a context flip for testing purposes without needing to wait for the notifier to completely fill up. This threshold is reset to the default value set by nouveau after each capture, and is exposed in a separate folder within each CRTC's debugfs directory labelled "nv_crc". Changes since v1: * Forgot to finish saving crc.h before saving, whoops. This just adds some corrections to the empty function declarations that we use if CONFIG_DEBUG_FS isn't enabled. Changes since v2: * Don't check return code from debugfs_create_dir() or debugfs_create_file() - Greg K-H Changes since v3: (no functional changes) * Fix SPDX license identifiers (checkpatch) * s/uint32_t/u32/ (checkpatch) * Fix indenting in switch cases (checkpatch) Changes since v4: * Remove unneeded param changes with nv50_head_flush_clr/set * Rebase Changes since v5: * Remove set but unused variable (outp) in nv50_crc_atomic_check() - Kbuild bot Signed-off-by: Lyude Paul <lyude@redhat.com> Reviewed-by: Ben Skeggs <bskeggs@redhat.com> Acked-by: Dave Airlie <airlied@gmail.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200627194657.156514-10-lyude@redhat.com |
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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.