On Thu, Jun 06, 2013 at 09:37:51PM +0300, Andy Shevchenko wrote: > On Thu, Jun 6, 2013 at 5:21 PM, Xenia Ragiadakou <burzalodowa@xxxxxxxxx> wrote: > > This patch adds a check on whether the host machine > > supports the xHC DMA address mask and sets the DMA > > mask for coherent DMA address allocation via an > > explicit call to dma_set_coherent_mask(). > > > > According to DMA-API-HOWTO, if coherent DMA address > > mask has not been set explicitly via dma_set_coherent_mask(), > > and the driver calls dma_alloc_coherent() or > > dma_pool_create() to allocate consistent DMA memory > > blocks, the consistent DMA mapping interface will > > return by default DMA addresses which are 32-bit > > addressable. > > > > Hence, if 64-bit DMA mapping is supported, it > > is appropriate to call dma_set_coherent_mask() > > with DMA_BIT_MASK(64) to take advantage of it. > > > > Also, according to DMA-API-HOWTO, dma_set_coherent_mask() > > is guaranteed to set successfully the same or a smaller > > mask as dma_set_mask(). > > It looks for me overcomplicated. Why? > We have *dma_mask and dma_coherent mask in the struct device. > First question, who is allocating memory for dma_mask? The xHCI driver is allocating memory for the host hardware structures, and the USB core is using the DMA mask of the host controller in order to move USB buffers into bounce buffers as necessary. The xHCI driver allocates memory from both DMA pools and with kmalloc. We need both calls to dma_set_coherent_mask() and dma_set_coherent_mask() to get 64-bit DMA addresses for both types of memory. > Second, in case of dma_mask == NULL, dma_set_mask fails with -EIO. It > doesn't mean we have no support of this one. How do you handle this > case? When would the dma_mask be NULL? Note that xHCI PCI hosts *must* be able to support DMA. > I think it's pretty simple to set dma_coherent_mask and then apply its > address to the dma_mask, because you set the same values anyway. I'm not quite understanding what you want to do. (I'll blame lack of sleep, sorry.) Can you write some pseudo code for me? Sarah Sharp -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
