RE: [PATCH 2/4] async_tx: kill tx_set_src and tx_set_dest methods

[Sosnowski, Maciej]

>From: Williams, Dan J 
>
>The tx_set_src and tx_set_dest methods were originally 
>implemented to allow
>an array of addresses to be passed down from async_xor to the dmaengine
>driver while minimizing stack overhead.  Removing these methods allows
>drivers to have all transaction parameters available at 'prep' 
>time, saves
>two function pointers in struct dma_async_tx_descriptor, and 
>reduces the
>number of indirect branches..
>
>A consequence of moving this data to the 'prep' routine is that
>multi-source routines like async_xor need temporary storage to 
>convert an
>array of linear addresses into an array of dma addresses.  In 
>order to keep
>the same stack footprint of the previous implementation the 
>input array is
>reused as storage for the dma addresses.  This requires that
>sizeof(dma_addr_t) be less than or equal to sizeof(void *).  As a
>consequence CONFIG_DMADEVICES now depends on 
>!CONFIG_HIGHMEM64G.  It also
>requires that drivers be able to make descriptor resources 
>available when
>the 'prep' routine is polled.
>
>Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>---

>From ioat_dma point of view this change just makes life easier as it
simplifies dma_async_tx_descriptor - it looks ok.

Maciej Sosnowski

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