Re: [PATCH] USB: use stack allocation for struct usb_ctrlrequest

Laurent Pinchart
2008-12-10T09:40:42Z

Hi Wu,

On Wednesday 10 December 2008, Wu Fengguang wrote:
> sizeof(struct usb_ctrlrequest) = 8, which is as small as the *dt pointer
> in a 64bit system.

The usb_ctrlrequest pointer is passed down to the hardware and must point to
DMA-able memory. For this reason you can't use the stack and must kmalloc()
the structure.

Best regards,

Laurent Pinchart

> Cc: Greg Kroah-Hartman <gregkh@suse.de>
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> ---
> drivers/usb/core/message.c | 27 ++++++++-------------------
> 1 file changed, 8 insertions(+), 19 deletions(-)
>
> --- linux-2.6.orig/drivers/usb/core/message.c
> +++ linux-2.6/drivers/usb/core/message.c
> @@ -130,26 +130,15 @@ int usb_control_msg(struct usb_device *d
> __u8 requesttype, __u16 value, __u16 index, void *data,
> __u16 size, int timeout)
> {
> - struct usb_ctrlrequest *dr;
> - int ret;
> -
> - dr = kmalloc(sizeof(struct usb_ctrlrequest), GFP_NOIO);
> - if (!dr)
> - return -ENOMEM;
> -
> - dr->bRequestType = requesttype;
> - dr->bRequest = request;
> - dr->wValue = cpu_to_le16p(&value);
> - dr->wIndex = cpu_to_le16p(&index);
> - dr->wLength = cpu_to_le16p(&size);
> + struct usb_ctrlrequest dr = {
> + .bRequestType = requesttype,
> + .bRequest = request,
> + .wValue = cpu_to_le16p(&value),
> + .wIndex = cpu_to_le16p(&index),
> + .wLength = cpu_to_le16p(&size),
> + };
>
> - /* dbg("usb_control_msg"); */
> -
> - ret = usb_internal_control_msg(dev, pipe, dr, data, size, timeout);
> -
> - kfree(dr);
> -
> - return ret;
> + return usb_internal_control_msg(dev, pipe, &dr, data, size, timeout);
> }
> EXPORT_SYMBOL_GPL(usb_control_msg);
>
> --
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