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authorAndy Shevchenko <andriy.shevchenko@linux.intel.com>2019-01-07 13:07:36 +0200
committerVinod Koul <vkoul@kernel.org>2019-01-07 17:57:13 +0530
commitd7dba6be0f31ae61f5f3296aa130f45d57d30f74 (patch)
treedf576295bc172e3c5ebcd22e2176411ad8997c51 /Documentation/devicetree/bindings/dma
parent87fe9ae84d7ba61df1f272e26df174e73b15cd74 (diff)
downloadlinux-d7dba6be0f31ae61f5f3296aa130f45d57d30f74.tar.bz2
dmaengine: dw: Remove misleading is_private property
The commit a9ddb575d6d6 ("dmaengine: dw_dmac: Enhance device tree support") introduces is_private property in uncertain understanding what does it mean. First of all, documentation defines DMA_PRIVATE capability as Documentation/crypto/async-tx-api.txt: The DMA_PRIVATE capability flag is used to tag dma devices that should not be used by the general-purpose allocator. It can be set at initialization time if it is known that a channel will always be private. Alternatively, it is set when dma_request_channel() finds an unused "public" channel. A couple caveats to note when implementing a driver and consumer: 1/ Once a channel has been privately allocated it will no longer be considered by the general-purpose allocator even after a call to dma_release_channel(). 2/ Since capabilities are specified at the device level a dma_device with multiple channels will either have all channels public, or all channels private. Documentation/driver-api/dmaengine/provider.rst: - DMA_PRIVATE The devices only supports slave transfers, and as such isn't available for async transfers. The capability had been introduced by the commit 59b5ec21446b ("dmaengine: introduce dma_request_channel and private channels") and some code didn't changed from that times ever. Taking into consideration above and the fact that on all known platforms Synopsys DesignWare DMA engine is attached to serve slave transfers, the DMA_PRIVATE capability must be enabled for this device unconditionally. Otherwise, as rightfully noticed in drivers/dma/at_xdmac.c: /* * Without DMA_PRIVATE the driver is not able to allocate more than * one channel, second allocation fails in private_candidate. */ because of of a caveats mentioned in above documentation excerpts. So, remove conditional around DMA_PRIVATE followed by removal leftovers. If someone wonders, DMA_PRIVATE can be not used if and only if the all channels of the DMA controller are supposed to serve memory-to-memory like operations. For example, EP93xx has two controllers, one of which can only perform memory-to-memory transfers Note, this change doesn't affect dmatest to be able to test such controllers. Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> (maintainer:SERIAL DRIVERS) Cc: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Vinod Koul <vkoul@kernel.org>
Diffstat (limited to 'Documentation/devicetree/bindings/dma')
-rw-r--r--Documentation/devicetree/bindings/dma/snps-dma.txt2
1 files changed, 0 insertions, 2 deletions
diff --git a/Documentation/devicetree/bindings/dma/snps-dma.txt b/Documentation/devicetree/bindings/dma/snps-dma.txt
index db757df7057d..0bedceed1963 100644
--- a/Documentation/devicetree/bindings/dma/snps-dma.txt
+++ b/Documentation/devicetree/bindings/dma/snps-dma.txt
@@ -23,8 +23,6 @@ Deprecated properties:
Optional properties:
-- is_private: The device channels should be marked as private and not for by the
- general purpose DMA channel allocator. False if not passed.
- multi-block: Multi block transfers supported by hardware. Array property with
one cell per channel. 0: not supported, 1 (default): supported.
- snps,dma-protection-control: AHB HPROT[3:1] protection setting.