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Since it's inception in 2012 it has been understood that the DRM GEM CMA helpers do not depend on CMA as the backend allocator. In fact the first bug fix to ensure the cma-helpers work correctly with an IOMMU backend appeared in 2014. However currently the documentation for drm_gem_cma_create() talks about "a contiguous chunk of memory" without making clear which address space it will be a contiguous part of. Additionally the CMA introduction is actively misleading because it only contemplates the CMA backend. This matters because when the device accesses the bus through an IOMMU (and don't use the CMA backend) then the allocated memory is contiguous only in the IOVA space. This is a significant difference compared to the CMA backend and the behaviour can be a surprise even to someone who does a reasonable level of code browsing (but doesn't find all the relevant function pointers ;-) ). Improve the kernel doc comments accordingly. Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> Reviewed-by: Lucas Stach <l.stach@pengutronix.de> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20220608135821.1153346-1-daniel.thompson@linaro.org
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.