On Tue, 14 May 2013, Sarah Sharp wrote: > On Wed, May 15, 2013 at 05:41:12AM +0300, Xenia Ragiadakou wrote: > > Hi Sarah, (again) > > > > Also I noticed that dma_set_coherent_mask() is not called somewhere, > > which according to DMA-API-HOWTO.txt, means the even if the DMA mask > > is set to 64 bits by dma_set_mask, dma_alloc_coherent and > > dma_pool_alloc wont return 64 bit addresses (32 MSbits wont be > > addressed). > > Another good question for Alan, and the USB and PCI list. This does sound like a bug. The PCI core initializes all devices by default with 32-bit masks for DMA and coherent DMA. (PCI-E, PCI-X, or other extensions may have more liberal policies.) If a larger mask can work, the driver is responsible for setting it up. > (Alan, Ksenia is one of the applicants for the FOSS Outreach Program for > Women that I've been coordinating: http://kernelnewbies.org/OPWIntro) > > We do allocate memory using DMA pools, and we do want 64-bit context > addresses if the xHCI host controller can handle it. > > The xHCI driver calls dma_set_mask, but not dma_set_coherent_mask(): > > temp = xhci_readl(xhci, &xhci->cap_regs->hcc_params); > if (HCC_64BIT_ADDR(temp)) { > xhci_dbg(xhci, "Enabling 64-bit DMA addresses.\n"); > dma_set_mask(hcd->self.controller, DMA_BIT_MASK(64)); > } else { > dma_set_mask(hcd->self.controller, DMA_BIT_MASK(32)); > } > > Alan, should it be calling dma_set_coherent_mask()? I think I may have > noticed the context addresses were never 64-bit addresses, but I didn't > think to look whether the host supported 64-bit addresses. I just > assumed it could only handle 32-bit addresses. If you're using 64-bit DMA then you almost certainly do want to call dma_set_coherent_mask(). On the plus side, it is guaranteed that if dma_set_mask() succeeds with a particular mask value then dma_set_coherent_mask() for the same mask value will also succeed. Ala Stern -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
