Hi Mark, > Sent: Tuesday, May 12, 2015 11:32 PM > > On 12/11/2014 09:58 PM, yoshihiro shimoda wrote: > > Hi Mark, > > > >> -----Original Message----- > >> From: linux-usb-owner@xxxxxxxxxxxxxxx [mailto:linux-usb-owner@xxxxxxxxxxxxxxx] On Behalf Of Mark Langsdorf > >> Sent: Wednesday, November 26, 2014 6:19 AM > >> To: linux-usb@xxxxxxxxxxxxxxx; mathias.nyman@xxxxxxxxx > >> Cc: mlangsdo@xxxxxxxxxx > >> Subject: [PATCH v3 1/2] make xhci platform driver use 64 bit or 32 bit DMA > >> > >> The xhci platform driver needs to work on systems that either only > >> support 64-bit DMA or only support 32-bit DMA. Attempt to set a > >> coherent dma mask for 64-bit DMA, and attempt again with 32-bit > >> DMA if that fails. > > > > I'm afraid but I have a comment about this patch. > > > > Since my environment (It's R-Car Gen2. It has ARM/CA15 and LPAE) has a > > restriction about DMA coherent, I intend to send some patches to avoid > > the restriction. And then, I found this patch. > > > > About my environment restriction is: > > - R-Car Gen2 can use LAPE. > > - So, dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64)); will not fail. > > - AXI address bus width of R-Car Gen2 xHCI controller is 32 bit. > > - However, The HCCPARAMS.AC64 is set to 1. > > > > So, in this environment, I think the xHCI driver should call > > dma_set_coherent(dev, DMA_BIT_MASK(32)) because AXI address bus width is 32 bit. > > However, in this case, the xHCI driver will call dma_set_coherent_mask(dev, DMA_BIT_MASK(64)) > > in line 4900 of drivers/usb/host/xhci.c: > > > > /* Set dma_mask and coherent_dma_mask to 64-bits, > > * if xHC supports 64-bit addressing */ > > if (HCC_64BIT_ADDR(xhci->hcc_params) && > > !dma_set_mask(dev, DMA_BIT_MASK(64))) { > > xhci_dbg(xhci, "Enabling 64-bit DMA addresses.\n"); > > dma_set_coherent_mask(dev, DMA_BIT_MASK(64)); > > } > > > > So, I intend to send some patches to add a quirk to this condition. > > However, if this patch is applied, I also need more patch for xhci-plat.c. > > > > Or, I misunderstand about the DMA-API? > > Hello, > > As best I understand your question, you would need to add a > quirk. I could change the patch to help you, if you'd like: > > - /* Initialize dma_mask and coherent_dma_mask to 32-bits */ > - ret = dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32)); > - if (ret) > - return ret; > - if (!pdev->dev.dma_mask) > - pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask; > - else > - dma_set_mask(&pdev->dev, DMA_BIT_MASK(32)); > + /* Try setting the coherent_dma_mask to 64 bits, then try 32 bits */ > + ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64)); > + if (ret || xhci_plat_lpae_dma()) { > + ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32)); > + if (ret) > + return ret; > + } > > bool xhci_plat_lpae_dma(void) would be a new function that returned true > if for your device and other devices that have 64-bit addressing in > general but only 32-bits of DMA. You would need to write that part. > > Would that be an acceptable solution? Thank you for the reply. Today I tried this patch, and then my environment could work correctly even if I don't add such a quirk "xhci_plat_lpae_dma()". I am investigating why but I didn't find a reason yet. So, if I find a reason and such a quirk is needed, I will submit such a patch. About this patch: Acked-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> Best regards, Yoshihiro Shimoda -- 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
