Verdin Mini RPMSG-Lite Increase Buffer Size

[Edward]

@swiss

Wait if I understand you correctly 512x512 is 256kB but the vring size in one direction is only 0x8000 as seen here:

256kB in comment in virtio_rpmsg_bus.c is totally misleading. Vring size isn’t multiple num_bufs * buf_size.
RPMSG_RING_SIZE is what fits vring size.

@swiss

So the RPMSG_RING_SIZE is not refering to the payload size but rather overhead information?

“Payload size”, if you meant RPMSG_BUF_SIZE, must using several tiny buffers from total amount of those tiny RPMSG_NUM_BUFS. Else 512*512 couldn’t fit 64k.

@swiss

But let’s go back to the concrete example: If I want to go from 512x512 to 1028x256, should I change the hardcoded 0x8000 ring size? I expected it to work without change because its still 256kB as before.

Yes, of course you have to change 0x8000. Please forget about misleading wrong number 256kB. It’s

Taking your own settings RPMSG_NUM_BUFS and RPMSG_BUF_SIZE, calculated RPMSG_RING_SIZE has to fit 20x8000=64k. And of course you new settings have to agree with device tree and M4 side settings for VRING starting addresses and VRING sizes.
For more or bigger buffers most likely you need to increase that magic 0x8000. On M4 this magic number is in VRING_SIZE define. Accordingly your adjacent M4 VDENx_VRING_BASE defines should differ by 2VRING_SIZE.