Messages in this thread | | | Subject | Re: [PATCH] dma-pool: use single atomic pool for both DMA zones | From | Robin Murphy <> | Date | Wed, 8 Jul 2020 17:20:16 +0100 |
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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.
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