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On i965/g4x IIR is edge triggered. So in order for IIR to notice that there is still a pending interrupt we have to force and edge in ISR. For the ISR/IIR pipe event bits we can do that by temporarily clearing all the PIPESTAT enable bits when we ack the status bits. This will force the ISR pipe event bit low, and it can then go back high when we restore the PIPESTAT enable bits. This avoids the following race: 1. stat = read(PIPESTAT) 2. an enabled PIPESTAT status bit goes high 3. write(PIPESTAT, enable|stat); 4. write(IIR, PIPE_EVENT) The end result is IIR==0 and ISR!=0. This can lead to nasty vblank wait/flip_done timeouts if another interrupt source doesn't trick us into looking at the PIPESTAT status bits despite the IIR PIPE_EVENT bit being low. Before i965 IIR was level triggered so this problem can't actually happen there. And curiously VLV/CHV went back to the level triggered scheme as well. But for simplicity we'll use the same i965/g4x compatible code for all platforms. Cc: stable@vger.kernel.org Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106033 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105225 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106030 Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180611200258.27121-1-ville.syrjala@linux.intel.com Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> |
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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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.