On 05/07/18 20:36, Christoph Hellwig wrote:
- BUG_ON(!ops);
- WARN_ON_ONCE(dev && !dev->coherent_dma_mask);
-
if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr))
return cpu_addr;
+ BUG_ON(!ops);
+ WARN_ON_ONCE(dev && !dev->coherent_dma_mask);
I think doing dma on a device without ops is completely broken no matter
what you think of it, so I very much disagree with that part of the change.
Also while I don't think not having a dma mask is a good idea even for
a driver purely using dma coherent pools. If the pools really are on
the device itself I can see why it might not matter, but for the case
commonly used on some ARM SOCs where we just reserve memory for certain
devices from a system pool it very much does matter.
There really is no good excuse to not set a coherent mask in the drivers.
Right, I was rather on the fence about this - on the one hand it is
objectively wrong per the API for drivers to call dma_alloc_coherent()
without a prior successful dma_set_coherent_mask() call, but then I
thought that in the case when they're *only* using it as a proxy for
dma_alloc_from_dev_coherent() and explicitly don't want regular
allocations from kernel memory to ever happen, then maybe it might be
somewhat reasonable. But indeed I hadn't really given enough thought to
the reserved-memory carveout case, where we definitely don't want to let
a legitimate warning be hidden on a developer's machine but hit by users
with different system configurations.
Fredrik, are you happy to fix up your driver to initialise a suitable
mask at probe time?
Robin.
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