On Fri, Dec 05, 2014 at 09:22:22AM +0000, Arend van Spriel wrote: > For our brcm80211 development we are working on getting brcmfmac driver > up and running on a Broadcom ARM-based platform. The wireless device is > a PCIe device, which is hooked up to the system behind a PCIe host > bridge, and we transfer information between host and device using a > descriptor ring buffer allocated using dma_alloc_coherent(). We mostly > tested on x86 and seen no issue. However, on this ARM platform > (single-core A9) we detect occasionally that the descriptor content is > invalid. When this occurs we do a dma_sync_single_for_cpu() and this is > retried a number of times if the problem persists. Actually, found out > that someone made a mistake by using virt_to_dma(va) to get the > dma_handle parameter. So probably we only provided a delay in the retry > loop. After fixing that a single call to dma_sync_single_for_cpu() is > sufficient. The DMA-API-HOWTO clearly states that: Does your system have an L2 cache? What's the SoC topology, can PCIe see such L2 cache (or snoop the L1 caches)? Also, are you certain that dma_alloc_coherent() ends up creating a non-cacheable mapping in Linux (this call translates to a function pointer call which may or may not create non-cacheable memory, depending on the "dma-coherent" property passed via DT). -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
