On 27/07/18 01:22, Grygorii Strashko wrote:
[...]

quoted

the result of this change is pretty strange as for me :(
Resulted code:

	/*
	 * If @dev is expected to be DMA-capable then the bus code that created
	 * it should have initialised its dma_mask pointer by this point. For
	 * now, we'll continue the legacy behaviour of coercing it to the
	 * coherent mask if not, but we'll no longer do so quietly.
	 */
	if (!dev->dma_mask) {
		dev_warn(dev, "DMA mask not set\n");
		dev->dma_mask = &dev->coherent_dma_mask;
^this will always produce warning in case of platform-bus or if there are no bus driver.
even if DT contains correct definition of dma-range
	}

	if (!size && dev->coherent_dma_mask)

^ coherent_dma_mask is zero, so size will not be calculated

pls, ignore this particular comment

quoted

		size = max(dev->coherent_dma_mask, dev->coherent_dma_mask + 1);
	else if (!size)
		size = 1ULL << 32;

	dev->dma_pfn_offset = offset;

	/*
	 * Limit coherent and dma mask based on size and default mask
	 * set by the driver.
	 */
	mask = DMA_BIT_MASK(ilog2(dma_addr + size - 1) + 1);
	dev->bus_dma_mask = mask;
	dev->coherent_dma_mask &= mask;

^^ if nobody set coherent_dma_mask before it will stay null forever unless drivers
will overwrite it. Again even if DT has correct definition for dma-range.

That is intentional. Consider a 32-bit device on a bus with an upstream 
DMA range of 40 bits (which could easily happen with e.g. PCI). If the 
firmware code gives that device 40-bit DMA masks and the driver doesn't 
change them, then DMA is not going to work correctly. Therefore the 
firmware code cannot safely make {coherent_}dma_mask larger than the 
default value passed in, and if the default is 0 then that should be 
fixed in whatever code created the device, not worked around later.

Robin.