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A typical use of cache maintenance functions is to force writeback of data which a device is about to read using DMA - for example a descriptor or command structure. Such users of cache maintenance functions require that operations on the cache have completed before they proceed to instruct a device to read memory. This requires that we place a completion barrier (ie. sync instruction) between the cache ops and whatever write informs the device to perform DMA. Whilst strictly speaking this isn't all users of the cache maintenance functions & we could instead place the barriers in the drivers that require them, it would be much more invasive to do so than to just have the barrier be the default by placing it in the cache functions themselves. The cost is low enough that it shouldn't matter to us in any rare cases that we use the cache functions when not performing DMA. Signed-off-by: Paul Burton <paul.burton@mips.com> Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com> Cc: u-boot@lists.denx.de |
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