Hi Mark,
> -----Original Message-----
> From: linux-usb-ow...@vger.kernel.org
> [mailto:linux-usb-ow...@vger.kernel.org] On Behalf Of Mark Langsdorf
> Sent: Wednesday, November 26, 2014 6:19 AM
> To: linux-usb@vger.kernel.org; mathias.ny...@intel.com
> Cc: mlang...@redhat.com
> 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?
Best regards,
Yoshihiro Shimoda
> Signed-off-by: Mark Langsdorf <mlang...@redhat.com>
> Tested-by: Mark Salter <msal...@redhat.com>
> ---
> Changes from v2:
> None
> Changes from v1:
> Consolidated to use dma_set_mask_and_coherent
> Got rid of the check against sizeof(dma_addr_t)
>
> drivers/usb/host/xhci-plat.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> index 3d78b0c..34cbf65 100644
> --- a/drivers/usb/host/xhci-plat.c
> +++ b/drivers/usb/host/xhci-plat.c
> @@ -96,14 +96,14 @@ static int xhci_plat_probe(struct platform_device *pdev)
> return ret;
> }
>
> - /* 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) {
> + ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
> + if (ret)
> + return ret;
> + }
> +
>
> hcd = usb_create_hcd(driver, &pdev->dev, dev_name(&pdev->dev));
> if (!hcd)
> --
> 1.9.3
>
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