vclog: Also try /dev/vc-mem for DMA copy

raspberrypi / utils

A collection of scripts and simple applications

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vclog: Also try /dev/vc-mem for DMA copy #36

Closed pelwell closed 11 months ago

pelwell commented 11 months ago

Allow for the fact that the dma_memcpy support may be provided by the vc_mem driver.

pelwell commented 11 months ago

https://github.com/raspberrypi/linux/pull/5651 is the corresponding kernel change.

timg236 commented 11 months ago

Does this work on Pi5 if there are no framebuffers? i.e. headless with max_framebuffers=0 ?

pelwell commented 11 months ago

This change (along with the kernel patch) is designed specifically for the no framebuffer case. However, Pi 5 is a bit special:

It has no memory hole, so it as no need for the DMA support.
The DMA controller's view of the world is different, so it doesn't need the high address alias bits setting.

The result is that the log appears, but at the cost of a logged kernel error:

[   30.137022] vc_mem_copy: invalid memory access 3ff16000 (fdb00000-ffc00000)

I think this patch in itself is fine, but the vc-mem driver should be modified to fail (or just memcpy) on non-2710 platforms.

timg236 commented 11 months ago

Yes, that makes sense.

pelwell commented 11 months ago

On that basis I'm going to merge this and revisit the vc_mem patch.

popcornmix commented 11 months ago

@XECDesign would be good to get this into RPiOS image soon. Currently vclog is broken on Pi2/Pi3. We also need a kernel bump, but it's safe to update this first.

XECDesign commented 11 months ago

Should be available in apt now