On Monday 11 February 2008, Klaus Pedersen wrote: > Because the dma_map_single() on ARM only flushes and invalidates > the cache-lines occupied by the transfer buffer, care should be > taken not to touch memory that share the same cache-lines before > starting the DMA transfer. > > In the McSPI driver dma_map_single() was called before the driver > was finished touching the spi_message and spi_transfer structures, > causing potential corruption of the transfer buffer. > > With a layout like this: > > struct spi_message read_msg; > u16 data[4]; Which is actually the source of the bug -- not omap2_mcspi. I probably wrote code like that at one point, since some of the earliest SPI framework code was done with omap1_uwire (a non-DMA driver, although ISTR the TX side could use DMA) where such idioms would not cause problems. In fact, I know for a fact that the ads7846 driver has that same bug. (Along with various others, which I'd like to see fixed first. Someone sent me a completely unreviewable and unmergeable patch that claims to fix "a bunch of stuff" in that driver. If anyone would like to help sort out the mess, let me know -- a lot of the problems seem to have come from that debounce logic added on Nokia's behalf.) I think that the tsc2046 + omap2_mcspi combination (on the omap2430 SDP?) won't hit that problem since none of its data buffers are large enough to kick in DMA. > - my (touchscreen) driver would get Best to fix your (touchscreen) driver ... > [ 5.875000] 0 0 1002 3334 > [ 6.695312] 0 0 1363 3234 > > after playing with the layout so that data[] starts on > a new cache-line I would get: > > [ 5.890625] 1507 788 1278 2720 > [ 5.890625] 1507 819 1242 2779 > > This patch solves the problem by moving the dma_map_single() > calls to just before the DMA is started. Best to just fix your driver. Have a separate data buffer. - Dave - To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
