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For platforms/outputs without hardware frame counters we can't call drm_crtc_accurate_vblank_count() when the vblank support is disabled or we just get a WARN due to the crtc timings (vblank->hwmode) being considered invalid. Note that until the pipe in question has been enabled and drm_crtc_set_max_vblank_count() has been called on it we would also take this path on platforms which have a working frame counter. So getting the WARN is rather likely on any platform unless you always boot with lots of displays plugged in. Also even on hardware with a working frame counter we may not be able to read the actual frame counter register on disabled pipes due the relevant power well being disabled. Ie. would just result in the unclaimed reg spew. So let's just avoid all this an directly report zero in case the pipe is disabled. Reported-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Reviewed-by: Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20210304170421.10901-3-ville.syrjala@linux.intel.com Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
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.