USB: set device dma_mask without reference to global data

Many USB host drivers contain code such as:

if (!pdev->dev.dma_mask)
        pdev->dev.dma_mask = &tegra_ehci_dma_mask;

... where tegra_ehci_dma_mask is a global. I suspect this code originated
in commit 4a53f4e "USB: ehci-tegra: add probing through device tree" and
was simply copied everywhere else.

This works fine when the code is built-in, but can cause a crash when the
code is in a module. The first module load sets up the dma_mask pointer,
but if the module is removed and re-inserted, the value is now non-NULL,
and hence is not updated to point at the new location, and hence points
at a stale location within the previous module load address, which in
turn causes a crash if the pointer is de-referenced.

The simplest way of solving this seems to be to copy the code from
ehci-platform.c, which uses the coherent_dma_mask as the target for the
dma_mask pointer.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Tony Prisk <linux@prisktech.co.nz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/usb/dwc3/dwc3-exynos.c b/drivers/usb/dwc3/dwc3-exynos.c
index a8afe6e26621..929e7dd6e58b 100644
--- a/drivers/usb/dwc3/dwc3-exynos.c
+++ b/drivers/usb/dwc3/dwc3-exynos.c
@@ -95,8 +95,6 @@ static int dwc3_exynos_remove_child(struct device *dev, void *unused)
         return 0;
 }
 
-static u64 dwc3_exynos_dma_mask = DMA_BIT_MASK(32);
-
 static int dwc3_exynos_probe(struct platform_device *pdev)
 {
         struct dwc3_exynos      *exynos;
@@ -118,7 +116,9 @@ static int dwc3_exynos_probe(struct platform_device *pdev)
          * Once we move to full device tree support this will vanish off.
          */
         if (!dev->dma_mask)
-                dev->dma_mask = &dwc3_exynos_dma_mask;
+                dev->dma_mask = &dev->coherent_dma_mask;
+        if (!dev->coherent_dma_mask)
+                dev->coherent_dma_mask = DMA_BIT_MASK(32);
 
         platform_set_drvdata(pdev, exynos);