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Re: [PATCH 42/44] powerpc/cell: use the dma_supported method for ops switching

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On Sun, Jun 18, 2017 at 06:50:27AM +1000, Benjamin Herrenschmidt wrote:
> What is your rationale here ? (I have missed patch 0 it seems).

Less code duplication, more modular dma_map_ops insteance.

> dma_supported() was supposed to be pretty much a "const" function
> simply informing whether a given setup is possible. Having it perform
> an actual switch of ops seems to be pushing it...

dma_supported() is already gone from the public DMA API as it doesn't
make sense to be called separately from set_dma_mask.  It will be
entirely gone in the next series after this one.

> What if a driver wants to test various dma masks and then pick one ?
> 
> Where does the API documents that if a driver calls dma_supported() it
> then *must* set the corresponding mask and use that ?

Where is the API document for _any_ of the dma routines? (A: work in
progress by me, but I need to clean up the mess of arch hooks before
it can make any sense)

> I don't like a function that is a "boolean query" like this one to have
> such a major side effect.
> 
> >From an API standpoint, dma_set_mask() is when the mask is established,
> and thus when the ops switch should happen.

And that's exactly what happens at the driver API level.  It just turns
out the dma_capable method is they way better place to actually
implement it, as the ->set_dma_mask method requires lots of code
duplication while not offering any actual benefit over ->dma_capable.
And because of that it's gone after this series.

In theory we could rename ->dma_capable now, but it would require a
_lot_ of churn.  Give me another merge window or two and we should
be down to be about 2 handful of dma_map_ops instance, at which point
we could do all this gratious renaming a lot more easily :)

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clean up and modularize arch dma_mapping interface V2 Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 44/44] powerpc: merge __dma_set_mask into dma_set_mask Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 38/44] arm: implement ->dma_supported instead of ->set_dma_mask Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 36/44] dma-mapping: remove HAVE_ARCH_DMA_SUPPORTED Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 42/44] powerpc/cell: use the dma_supported method for ops switching Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
    Re: [PATCH 42/44] powerpc/cell: use the dma_supported method for  ops switching Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-06-17 23:00 +0200
      Re: [PATCH 42/44] powerpc/cell: use the dma_supported method for ops  switching Christoph Hellwig <hch@infradead.org> - 2017-06-18 09:20 +0200
        Re: [PATCH 42/44] powerpc/cell: use the dma_supported method for  ops switching Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-06-18 12:00 +0200
  [PATCH 27/44] sparc: remove leon_dma_ops Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 31/44] hexagon: remove arch-specific dma_supported implementation Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 34/44] arm: remove arch specific dma_supported implementation Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 29/44] dma-noop: remove dma_supported and mapping_error methods Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 40/44] tile: remove dma_supported and mapping_error methods Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 41/44] powerpc/cell: clean up fixed mapping dma_ops initialization Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 33/44] openrisc: remove arch-specific dma_supported implementation Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 39/44] xen-swiotlb: remove xen_swiotlb_set_dma_mask Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 17/44] hexagon: switch to use ->mapping_error for error reporting Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 35/44] x86: remove arch specific dma_supported implementation Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 32/44] hexagon: remove the unused dma_is_consistent prototype Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 13/44] openrisc: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 37/44] mips/loongson64: implement ->dma_supported instead of ->set_dma_mask Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 15/44] xtensa: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 24/44] x86: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 28/44] sparc: remove arch specific dma_supported implementations Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 02/44] ibmveth: properly unwind on init errors Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 01/44] firmware/ivc: use dma_mapping_error Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 43/44] dma-mapping: remove the set_dma_mask method Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 30/44] dma-virt: remove dma_supported and mapping_error methods Christoph Hellwig <hch@lst.de> - 2017-06-16 20:20 +0200
  [PATCH 26/44] dma-mapping: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 16/44] arm64: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 21/44] powerpc: implement ->mapping_error Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 14/44] sh: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 19/44] s390: implement ->mapping_error Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 25/44] arm: implement ->mapping_error Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 23/44] x86/calgary: implement ->mapping_error Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 06/44] iommu/dma: don't rely on DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
    Re: [PATCH 06/44] iommu/dma: don't rely on DMA_ERROR_CODE Robin Murphy <robin.murphy@arm.com> - 2017-06-19 17:20 +0200
  [PATCH 18/44] iommu/amd: implement ->mapping_error Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 20/44] sparc: implement ->mapping_error Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 10/44] ia64: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 08/44] xen-swiotlb: implement ->mapping_error Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 03/44] dmaengine: ioat: don't use DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
    Re: [PATCH 03/44] dmaengine: ioat: don't use DMA_ERROR_CODE Alexander Duyck <alexander.duyck@gmail.com> - 2017-06-16 22:50 +0200
      Re: [PATCH 03/44] dmaengine: ioat: don't use DMA_ERROR_CODE Christoph Hellwig <hch@infradead.org> - 2017-06-18 09:10 +0200
  [PATCH 04/44] drm/exynos: don't use DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 09/44] c6x: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 07/44] xen-swiotlb: consolidate xen_swiotlb_dma_ops Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 11/44] m32r: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 22/44] x86/pci-nommu: implement ->mapping_error Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 12/44] microblaze: remove DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200
  [PATCH 05/44] drm/armada: don't abuse DMA_ERROR_CODE Christoph Hellwig <hch@lst.de> - 2017-06-16 20:30 +0200

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