Linux-USB Archive on lore.kernel.org
 help / color / Atom feed
From: Alan Stern <stern@rowland.harvard.edu>
To: Suwan Kim <suwan.kim027@gmail.com>
Cc: shuah@kernel.org, <valentina.manea.m@gmail.com>,
	<gregkh@linuxfoundation.org>, <linux-usb@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] usbip: Implement map_urb_for_dma function for vhci to skip dma mapping
Date: Tue, 18 Jun 2019 11:30:34 -0400 (EDT)
Message-ID: <Pine.LNX.4.44L0.1906181129450.1659-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20190618142817.16844-1-suwan.kim027@gmail.com>

On Tue, 18 Jun 2019, Suwan Kim wrote:

> vhci doesn’t do dma for remote device. Actually, the real dma
> operation is done by network card driver. So, vhci doesn’t use and
> need dma address of transfer buffer of urb.
> 
> But hcd provides dma mapping function by defualt in usb_hcd_submit_urb()
> and it causes unnecessary dma mapping which will be done again at
> NIC driver and it wastes CPU cycles. So, implement map_urb_for_dma
> function for vhci in order to skip the dma mapping procedure.
> 
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
>  drivers/usb/usbip/vhci_hcd.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> index 667d9c0ec905..9df4d9e36788 100644
> --- a/drivers/usb/usbip/vhci_hcd.c
> +++ b/drivers/usb/usbip/vhci_hcd.c
> @@ -1287,6 +1287,13 @@ static int vhci_free_streams(struct usb_hcd *hcd, struct usb_device *udev,
>  	return 0;
>  }
>  
> +static int vhci_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> +			    gfp_t mem_flags)
> +{
> +	dev_dbg(hcd->self.controller, "vhci does not map urb for dma\n");
> +	return 0;
> +}
> +
>  static const struct hc_driver vhci_hc_driver = {
>  	.description	= driver_name,
>  	.product_desc	= driver_desc,
> @@ -1302,6 +1309,7 @@ static const struct hc_driver vhci_hc_driver = {
>  	.urb_dequeue	= vhci_urb_dequeue,
>  
>  	.get_frame_number = vhci_get_frame_number,
> +	.map_urb_for_dma = vhci_map_urb_for_dma,
>  
>  	.hub_status_data = vhci_hub_status,
>  	.hub_control    = vhci_hub_control,

If the goal is to avoid wasting CPU cycles, you probably should have a 
vhci_unmap_urb_for_dma routine as well.

Alan Stern


  reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-18 14:28 Suwan Kim
2019-06-18 15:30 ` Alan Stern [this message]
2019-06-19  8:16   ` Suwan Kim

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=Pine.LNX.4.44L0.1906181129450.1659-100000@iolanthe.rowland.org \
    --to=stern@rowland.harvard.edu \
    --cc=gregkh@linuxfoundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-usb@vger.kernel.org \
    --cc=shuah@kernel.org \
    --cc=suwan.kim027@gmail.com \
    --cc=valentina.manea.m@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-USB Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-usb/0 linux-usb/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-usb linux-usb/ https://lore.kernel.org/linux-usb \
		linux-usb@vger.kernel.org linux-usb@archiver.kernel.org
	public-inbox-index linux-usb


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-usb


AGPL code for this site: git clone https://public-inbox.org/ public-inbox