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raspberrypi / firmware

This repository contains pre-compiled binaries of the current Raspberry Pi kernel and modules, userspace libraries, and bootloader/GPU firmware.
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VCHIQ mailbox channel is undocumented #1137

Open ptesarik opened 5 years ago

ptesarik commented 5 years ago

There is a wiki page about the mailbox channels (https://github.com/raspberrypi/firmware/wiki/Mailboxes), but no explanation of the VCHIQ interface. The Linux driver has been in staging for years, and more information on the interface is needed to get it promoted as a 'real' kernel driver.

JamesH65 commented 5 years ago

If this https://github.com/raspberrypi/documentation/tree/JamesH65-mailbox_docs/configuration/mailboxes doesn't help, I don't think there is much that can be done in the near future.

What specific information is needed to make a 'real' kernel driver ? Although I suspect our definition of real may differ, and I also doubt that any extra docs will help get it out of staging.

ptesarik commented 5 years ago

Well, the current (upstream) driver may cause data corruption (according to the TODO). I suspect this can happen when the VPU (firmware) writes to a buffer that has already been freed by the ARM core.

Another point in the same TODO file is:

6) Documentation

A short top-down description of this driver's architecture (function of kthreads, userspace, limitations) could be very helpful for reviewers.

ptesarik commented 5 years ago

If this https://github.com/raspberrypi/documentation/tree/JamesH65-mailbox_docs/configuration/mailboxes doesn't help, I don't think there is much that can be done in the near future.

If nothing else, tag 0x00048010 (RPI_FIRMWARE_VCHIQ_INIT) is missing from this documentation.

ptesarik commented 5 years ago

Please review raspberrypi/documentation#1150 for starters. However, some documentation of the VCHIQ mechanism is also desirable (message format, doorbell usage, etc.), so I'd like to leave this issue open even if you merge my PR.

lategoodbye commented 5 years ago

Please also refer to this comment https://github.com/raspberrypi/linux/issues/2730#issuecomment-442599071