On Wednesday, August 24, 2011 13:27:05 Anton Staaf wrote: > On Wed, Aug 24, 2011 at 6:25 AM, Wolfgang Denk wrote: > > Lukasz Majewski wrote: > >> 4. get_dcache_line_size() can be simply defined as > >> #define get_dcache_line_size() CONFIG_SYS_CACHE_LINE_SIZE if we > >> _really_ want to save a few bytes. > > > > Actually I fail to understand why we would ever need > > get_dcache_line_size() in a boot loader. > > It is required so that we can correctly allocate buffers that will be > used by DMA engines to read or write data. The reason that these > buffers need to be cache line size aligned is because unaligned cache > invalidates are not possible to do in a safe way. The problem is that > invalidating a partial cache line requires invalidating the entire > line. And the other part of the line can contain nearby variables > (especially if the buffer is stack allocated), so we have to first > flush the cache line to be safe. However, that flush will clobber the > values that the DMA engine wrote to main memory that are not reflected > in the cache.
right, and that's why i want to "hide" it be hind a "dma buffer allocate" API so that people can just say "i want a dma safe buffer" rather than having to delve into these details. they'll inevitable get confused and screw it up. ;) -mike
signature.asc
Description: This is a digitally signed message part.
_______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
