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The A5XX GPU powers on in "secure" mode. In secure mode the GPU can only render to buffers that are marked as secure and inaccessible to the kernel and user through a series of hardware protections. In practice secure mode is used to draw things like a UI on a secure video frame. In order to switch out of secure mode the GPU executes a special shader that clears out the GMEM and other sensitve registers and then writes a register. Because the kernel can't be trusted the shader binary is signed and verified and programmed by the secure world. To do this we need to read the MDT header and the segments from the firmware location and put them in memory and present them for approval. For targets without secure support there is an out: if the secure world doesn't support secure then there are no hardware protections and we can freely write the SECVID_TRUST register from the CPU. We don't have 100% confidence that we can query the secure capabilities at run time but we have enough calls that need to go right to give us some confidence that we're at least doing something useful. Of course if we guess wrong you trigger a permissions violation which usually ends up in a system crash but thats a problem that shows up immediately. [v2: use child device per Bjorn] [v3: use generic MDT loader per Bjorn] [v4: use managed dma functions and ifdefs for the MDT loader] [v5: Add depends for QCOM_MDT_LOADER] Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org> Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org> [robclark: fix Kconfig to use select instead of depends + #if IS_ENABLED()] Signed-off-by: Rob Clark <robdclark@gmail.com> |
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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.