Messages in this thread | | | Date | Sun, 21 Sep 2008 21:50:18 +0200 (CEST) | From | Guennadi Liakhovetski <> | Subject | Re: dmaengine.c: question about device_alloc_chan_resources |
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On Sun, 21 Sep 2008, Haavard Skinnemoen wrote:
> > 2/ What about platform specific concerns where dma_cap_mask_t is not > > descriptive enough e.g. only one memcpy channel can address a certain > > bus? Currently a client implementation can have some intelligence to > > return DMA_DUP for channels that do not have the platform capability. > > Currently, clients requesting the DMA_SLAVE capability can specify > which particular DMA device they need. Would it make sense to allow > other clients to do that as well?
This is how it is documented in dmaengine.h:
* @slave: data for preparing slave transfer. Must be non-NULL iff the * DMA_SLAVE capability is requested.
But, looking at dma_client_chan_alloc() it seems, any client requesting a channel can provide a slave and link it to a specific dma_dev, regardless what capabilities the client is requesting, or am I missing something? If so, then yes, please, let's allow all do this. Wouldn't it be better to move the .dma_dev member to dma_client?
> Also, struct dma_slave can be extended with > controller-/platform-specific fields. Maybe we need a similar mechanism > for passing platform-specific constraints when requesting "regular" > channels?
As far as I understand, this extension can only be done by "wrapping" dma_slave with driver-specific data:
* If dma_dev is non-NULL, the client can not be bound to other DMA * masters than the one corresponding to this device. The DMA master * driver may use this to determine if there is controller-specific * data wrapped around this struct. Drivers of platform code that sets * the dma_dev field must therefore make sure to use an appropriate * controller-specific dma slave structure wrapping this struct.
i.e., there is no "void *priv" or similar. So, the same "wrapping" can be used with dma_client, even more conveniently so, if we move .dma_dev into it.
Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer
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