Re: [PATCH] dma-pool: use single atomic pool for both DMA zones
From: Robin Murphy
Date: Wed Jul 08 2020 - 12:20:20 EST
On 2020-07-08 16:36, Christoph Hellwig wrote:
On Wed, Jul 08, 2020 at 12:35:34PM +0200, Nicolas Saenz Julienne wrote:
Which allows me to switch between ACPI/DT on the machine. In DT mode it
works fine now,
Nice, would that count as a Tested-by from you?
but with ACPI I continue to have failures unless I
disable CMA via cma=0 on the kernel command line.
Yes, I see why, in atomic_pool_expand() memory is allocated from CMA without
checking its correctness. That calls for a separate fix. I'll try to think of
something.
I think we need a dma_coherent_ok for the allocations from the
pool and then fall back to the next better one to get started. And
yes, CMA is a bit of a mess, that generally needs better checks.
Yeah, another thought that came to mind later is that iommu-dma can use
pages from any pool regardless of the device's DMA mask, so we could
stand to be a lot less restrictive in that case too.
Perhaps it is better to just bite the bullet, keep the straightforward
one-pool-per-zone setup, and implement the dma_coherent_ok() type
fallback logic. More complexity for dma_alloc_from_pool(), but
everything else stays nice and simple - lose the assumption that
dev_to_pool() can work for this and and just let callers pass an
allocation mask directly, and have dma_free_from_pool() simply check all
available pools.
Robin.