1) Import drivers using VCHI.
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VCHI is just a tool to let drivers talk to the firmware. Here are
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some of the ones we want:
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- vc_mem (https://github.com/raspberrypi/linux/blob/rpi-4.4.y/drivers/char/broadcom/vc_mem.c)
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This driver is what the vcdbg userspace program uses to set up its
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requests to the firmware, which are transmitted across VCHIQ. vcdbg
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is really useful for debugging firmware interactions.
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- VCSM (https://github.com/raspberrypi/linux/tree/rpi-4.4.y/drivers/char/broadcom/vc_sm)
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This driver is used for talking about regions of VC memory across
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firmware protocols including VCHI. We'll want to extend this driver
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to manage these buffers as dmabufs so that we can zero-copy import
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camera images into vc4 for rendering/display.
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2) Garbage-collect unused code
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One of the reasons this driver wasn't upstreamed previously was that
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there's a lot code that got built that's probably unnecessary these
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days. Once we have the set of VCHI-using drivers we want in tree, we
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should be able to do a sweep of the code to see what's left that's
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unused.
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3) Make driver more portable
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Building this driver with arm/multi_v7_defconfig or arm64/defconfig
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leads to data corruption during the following command:
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vchiq_test -f 1
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This should be fixed.
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4) Fix kernel module support
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Even the VPU firmware doesn't support a VCHI re-connect, the driver
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should properly handle a module unload. This also includes that all
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resouces must be freed (kthreads, debugfs entries, ...) and global
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variables avoided.
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5) Cleanup logging mechanism
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The driver should probably be using the standard kernel logging mechanisms
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such as dev_info, dev_dbg, and friends.
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6) Documentation
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A short top-down description of this driver's architecture (function of
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kthreads, userspace, limitations) could be very helpful for reviewers.
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