From: shuah <shuah@kernel.org>
To: Suwan Kim <suwan.kim027@gmail.com>,
valentina.manea.m@gmail.com, gregkh@linuxfoundation.org,
stern@rowland.harvard.edu
Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
shuah <shuah@kernel.org>
Subject: Re: [PATCH v3 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci
Date: Fri, 2 Aug 2019 16:22:27 -0600 [thread overview]
Message-ID: <c23b3ac1-68d9-bc1e-610b-955988e11055@kernel.org> (raw)
In-Reply-To: <20190802173651.22247-2-suwan.kim027@gmail.com>
On 8/2/19 11:36 AM, Suwan Kim wrote:
> vhci doesn’t do DMA for remote device. Actually, the real DMA
> operation is done by network card driver. vhci just passes virtual
> address of the buffer to the network stack, so vhci doesn’t use and
> need dma address of the buffer of the URB.
>
> But HCD provides DMA mapping and unmapping function by default.
> Moreover, it causes unnecessary DMA mapping and unmapping which
> will be done again at the NIC driver and it wastes CPU cycles.
> So, implement map_urb_for_dma and unmap_urb_for_dma function for
> vhci in order to skip the DMA mapping and unmapping procedure.
>
> When it comes to supporting SG for vhci, it is useful to use native
> SG list (urb->num_sgs) instead of mapped SG list because DMA mapping
> fnuction can adjust the number of SG list (urb->num_mapped_sgs).
> And vhci_map_urb_for_dma() prevents isoc pipe from using SG as
> hcd_map_urb_for_dma() does.
>
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
> drivers/usb/usbip/vhci_hcd.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> index 000ab7225717..c62f7fa8118c 100644
> --- a/drivers/usb/usbip/vhci_hcd.c
> +++ b/drivers/usb/usbip/vhci_hcd.c
> @@ -1288,6 +1288,22 @@ 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)
> +{
> + if (usb_endpoint_xfer_isoc(&urb->ep->desc) && urb->num_sgs) {
> + WARN_ON(1);
Don't add WARN_ON. I cleaned them all up recently and don't want new
ones added.
thanks,
-- Shuah
next prev parent reply other threads:[~2019-08-02 22:22 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-02 17:36 [PATCH v3 0/2] usbip: Implement SG support Suwan Kim
2019-08-02 17:36 ` [PATCH v3 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci Suwan Kim
2019-08-02 22:22 ` shuah [this message]
2019-08-05 5:23 ` Suwan Kim
2019-08-05 15:08 ` shuah
2019-08-02 17:36 ` [PATCH v3 2/2] usbip: Implement SG support to vhci-hcd and stub driver Suwan Kim
2019-08-02 22:41 ` shuah
2019-08-05 8:04 ` Suwan Kim
2019-08-05 15:07 ` shuah
2019-08-02 22:44 ` [PATCH v3 0/2] usbip: Implement SG support shuah
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