I don't know as I did not see both next to each other, but previously I thought 8Mbps SPI with 240x240 must be pathetic (see this forum post and the video there) but this is not so bad.
There is no DMA for 8-bit parallel mode so the code must do both at once - palette conversion and/or scaling and sending to display. Wth DMA you can compute first block of pixels in advance and then both can run in parallel. With larger blocks than just few bytes the DMA could amost reach maximum theoretical 8Mbps speed. So e.g filling 240x240 in 12 bits (1.5bytes per pixel) takes 96ms when using dma in 24byte blocks.
Even if there is mode when the DMA does not stop and can send several buffers (or same buffer) repeatedly on its own automatically, for some reason letting it loop over 6 byte buffers or 24byte buffers in such mode is a difference. With just the 6 byte buffer in code above it it was still like 125ms ~= same as sending it without DMA, and the 3byte buffer was even slower.
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