linux-kernel - Re: [PATCH v2 2/3] USB: ehci-tegra: fix inefficient copy of unaligned buffers

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Date:	Thu, 23 Apr 2015 16:31:51 +0200
From:	Frans Klaver <fransklaver@...il.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Felipe Balbi <balbi@...com>,
	Alan Stern <stern@...land.harvard.edu>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2 2/3] USB: ehci-tegra: fix inefficient copy of unaligned buffers

On Thu, Apr 23, 2015 at 4:06 PM, Johan Hovold <johan@...nel.org> wrote:
> Make sure only to copy any actual data rather than the whole buffer,
> when releasing the temporary buffer used for unaligned non-isochronous
> transfers.
>
> Compile-tested only.
>
> Signed-off-by: Johan Hovold <johan@...nel.org>
> ---
>  drivers/usb/host/ehci-tegra.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
> index ff9af29b4e9f..4031b372008e 100644
> --- a/drivers/usb/host/ehci-tegra.c
> +++ b/drivers/usb/host/ehci-tegra.c
> @@ -304,6 +304,7 @@ struct dma_aligned_buffer {
>  static void free_dma_aligned_buffer(struct urb *urb)
>  {
>         struct dma_aligned_buffer *temp;
> +       size_t length;
>
>         if (!(urb->transfer_flags & URB_ALIGNED_TEMP_BUFFER))
>                 return;
> @@ -311,9 +312,14 @@ static void free_dma_aligned_buffer(struct urb *urb)
>         temp = container_of(urb->transfer_buffer,
>                 struct dma_aligned_buffer, data);
>
> -       if (usb_urb_dir_in(urb))
> -               memcpy(temp->old_xfer_buffer, temp->data,
> -                      urb->transfer_buffer_length);
> +       if (usb_urb_dir_in(urb)) {
> +               if (usb_pipeisoc(urb->pipe))
> +                       length = urb->transfer_buffer_length;
> +               else
> +                       length = urb->actual_length;
> +
> +               memcpy(temp->old_xfer_buffer, temp->data, length);
> +       }
>         urb->transfer_buffer = temp->old_xfer_buffer;
>         kfree(temp->kmalloc_ptr);

Out of curiosity: any reason not to declare that length variable
inside this new compound?

Thanks,
Frans
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