Messages in this thread | | | Date | Tue, 31 Jul 2012 09:27:49 +0200 | Subject | Re: About dma_sync_single_for_{cpu,device} | From | Karl Beldan <> |
| |
On 7/31/12, Clemens Ladisch <clemens@ladisch.de> wrote: > Karl Beldan wrote: >> To tx a chunk of data from the SoC => network device, we : >> - prepare a buffer with a leading header embedding a pattern, >> - trigger the xfer and wait for an irq >> // The device updates the pattern and then triggers an irq >> - upon irq we check the pattern for the xfer completion >> >> I was expecting the following to work: >> addr = dma_map_single(dev, buffer, size, DMA_TO_DEVICE); > > Of both the CPU and the device write to the buffer, you must use > DMA_BIDIRECTIONAL. > Hi Clemens,
This does not work (tested) : seems to me BIDIRECTIONAL would just add invalidate, and invalidate before the ram has been updated, as stated, does not work. In fact the immediately following sync_for_device is intended to cater for what DMA_BIDIRECTIONAL would provide (though it is not implementation agnostic), only invalidating a smaller address range.
Regards,
Karl
| |