Re: [PATCH v7 1/2] usb: make xhci platform driver use 64 bit or 32 bit DMA

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On 31.08.2015 21:58, Duc Dang wrote:
On Thu, Aug 20, 2015 at 12:38 PM, Duc Dang <dhdang@xxxxxxx> wrote:
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.

[dhdang: regenerate the patch over 4.2-rc5 and address new comments]
Signed-off-by: Mark Langsdorf <mlangsdo@xxxxxxxxxx>
Tested-by: Mark Salter <msalter@xxxxxxxxxx>
Signed-off-by: Duc Dang <dhdang@xxxxxxx>

---
Changes from v6:
         -Add WARN_ON if dma_mask is NULL
         -Use dma_coerce_mask_and_coherent to assign
         dma_mask and coherent_dma_mask

Changes from v5:
         -Change comment
         -Assign dma_mask to coherent_dma_mask if dma_mask is NULL
         to make sure dma_set_mask_and_coherent does not fail prematurely.

Changes from v4:
         -None

Changes from v3:
         -Re-generate the patch over 4.2-rc5
         -No code change.

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 | 21 +++++++++++++--------
  1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index 890ad9d..e4c7f9d 100644
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -93,14 +93,19 @@ static int xhci_plat_probe(struct platform_device *pdev)
         if (irq < 0)
                 return -ENODEV;

-       /* 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));
+       /* Throw a waring if broken platform code didn't initialize dma_mask */
+       WARN_ON(!pdev->dev.dma_mask);
+       /*
+        * Try setting dma_mask and coherent_dma_mask to 64 bits,
+        * then try 32 bits
+        */
+       ret = dma_coerce_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
+       if (ret) {
+               ret = dma_coerce_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)
--
1.9.1


Hi Greg, Arnd, Russell,

Do you have any more comment about this patch set?


I'm not sure I fully understand why we need to try the 64 bit DMA mask in platform probe.

As I understood it we just want to have some DMA mask set before calling usb_create_hcd()
to make sure USB core gets the "uses_dma" flag set and dma_set_mask() won't fail because of
missing dev->dma_mask.

The correct DMA mask is set later in xhci_gen_setup()

We also need to make sure the controller supports 64bit addressing capability before setting a 64 bit DMA mask.
(bit 0 in HCCPARAMS)

So for platform devices it goes look go this:

xhci_plat_probe()
  usb_create_hcd()
    usb_create_shared_hcd()
      hcd->self.uses_dma = (dev->dma_mask != NULL);
  usb_add_hcd()
    hcd->driver->reset()  (.reset = xhci_plat_setup)
      xhci_plat_setup()
        xhci_gen_setup()
          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));
          }

or do we end up with dev->dma_mask = NULL on 64-bit DMA only after trying to set it to 32 in xhci_plat_probe(),
and thus also failing the dma_set_mask() in xhci_gen_setup()?

-Mathias










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