On Thu, 20 Jan 2011, Robert Morell wrote:
> The Tegra2 USB controller doesn't properly deal with misaligned DMA
> buffers, causing corruption. This is especially prevalent with USB
> network adapters, where skbuff alignment is often in the middle of a
> 4-byte dword.
>
> To avoid this, allocate a temporary buffer for the DMA if the provided
> buffer isn't sufficiently aligned.
>
> Signed-off-by: Robert Morell <rmorell@xxxxxxxxxx>
> ---
> drivers/usb/host/ehci-tegra.c | 92 +++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 92 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
> index 2341904..7cdfc65 100644
> --- a/drivers/usb/host/ehci-tegra.c
> +++ b/drivers/usb/host/ehci-tegra.c
> @@ -32,6 +32,8 @@
> #define TEGRA_USB_USBMODE_HOST (3 << 0)
> #define TEGRA_USB_PORTSC1_PTC(x) (((x) & 0xf) << 16)
>
> +#define TEGRA_USB_DMA_ALIGN 32
> +
> struct tegra_ehci_context {
> bool valid;
> u32 command;
> @@ -461,6 +463,94 @@ static int tegra_ehci_bus_resume(struct usb_hcd *hcd)
> }
> #endif
>
> +struct temp_buffer {
> + void *kmalloc_ptr;
> + void *old_xfer_buffer;
> + u8 data[0];
> +};
> +
> +static void free_temp_buffer(struct urb *urb, int status)
> +{
> + enum dma_data_direction dir;
> + struct temp_buffer *temp;
> +
> + if (!(urb->transfer_flags & URB_ALIGNED_TEMP_BUFFER))
> + return;
> +
> + dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> +
> + temp = container_of(urb->transfer_buffer, struct temp_buffer,
> + data);
> +
> + if (dir == DMA_FROM_DEVICE && !status)
> + memcpy(temp->old_xfer_buffer, temp->data,
> + urb->transfer_buffer_length);
Even if status is nonzero, there may be valid data in the buffer. You
should skip that test.
No other problems that I can see.
Alan Stern
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