quoted

Some people wanted the possibility to set the DMA mask as this USB2 CI
driver does not do specific Berlin operation and can be reused later.
I don't particularly need to call dma_coerce_mask_and_coherent() in my
case, as far as I know.

Ok, just remove the call then and rely on the default mask.

quoted

They can maybe give the restrictions they might want to put on the DMA
mask.

If the restriction is from the bus, it should get handled automatically
by the device probe as long as the correct dma-ranges property is there
(though we have a small bug there at the moment). If there is a variation
of ci13xxx that can't do 32-bit DMA, that should use a different
compatible string and pass a fixed mask into dma_set_mask_and_coherent()
based on the device.

Correct me if my below understanding is wrong please.

For three chipidea users:
user_a: don't need dma mask
user_b: dma mask value is dma_mask_b
user_c: dma mask value is dma_mask_c

We don't need to call dma_coerce_mask_and_coherent() at generic chipidea
glue driver, and set dma-ranges as dma_mask_b at user_b's dts, and set
dma-ranges as dma_mask_c at user_c's dts.

Peter