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The PL330 is hard-wired such that instruction fetches on both the manager and channel threads go out onto the bus with the "privileged" bit set. This can become troublesome once there is an IOMMU or other form of memory protection downstream, since those will typically be programmed by the DMA mapping subsystem in the expectation of normal unprivileged transactions (such as the PL330 channel threads' own data accesses as currently configured by this driver). To avoid the case of, say, an IOMMU blocking an unexpected privileged transaction with a permission fault, use the newly-introduced DMA_ATTR_PRIVILEGED attribute for the mapping of our microcode buffer. That way the DMA layer can do whatever it needs to do to make things continue to work as expected on more complex systems. Cc: Dan Williams <dan.j.williams@intel.com> Cc: Vinod Koul <vinod.koul@intel.com> Reviewed-by: Robin Murphy <robin.murphy@arm.com> Tested-by: Robin Murphy <robin.murphy@arm.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Vinod Koul <vinod.koul@intel.com> Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org> [rm: remove now-redundant local variable, clarify commit message] Signed-off-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com> |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.