Re: [Patch] dma_sync_to_device

[Deepak Saxena <dsaxena@plexity.net>]

On Feb 11 2004, at 11:08, David S. Miller was caught saying:
> New sequence:
> 
> 1) pci_map_single(..., DMA_TO_DEVICE).  Flush dirty data from cpu caches to memory,
>    so device may see it.
> 
> 2) device reads buffer
> 
> 3) pci_dma_sync_single(... DMA_TO_DEVICE).  If PCI controller has caches, flush them.
> 
> 4) CPU writes new buffer data.
> 
> 5) pci_dma_sync_device_single(... DMA_TO_DEVICE).  Like #1, flush dirty data from cpu
>    caches to memory.
> 
> 6) Device reads buffer.
> 
> Still disagree? :-)

/me groks now. I am assuming this is a 2.7 thing as it is
reinterpreting/redefining the API. In ARM, pci_dma_sync_single() does
a cache flush, which is why I was confused asked about two cache flushes.
What you are proposing is that by definition pci_dma_sync_* syncs 
bridges caches with system memory, while pci_dma_sync_device_* syncs 
the CPU's cache with system memory.

This will definetely confuse a lot of driver writers. 

~Deepak

-- 
Deepak Saxena - dsaxena at plexity dot net - http://www.plexity.net/