Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 5 Aug 2019 14:23:58 +0900
From:   Suwan Kim <suwan.kim027@gmail.com>
To:     shuah <shuah@kernel.org>
Cc:     valentina.manea.m@gmail.com, gregkh@linuxfoundation.org,
        stern@rowland.harvard.edu, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/2] usbip: Skip DMA mapping and unmapping for urb at
 vhci
Message-ID: <20190805052358.GA8904@localhost.localdomain>
References: <20190802173651.22247-1-suwan.kim027@gmail.com>
 <20190802173651.22247-2-suwan.kim027@gmail.com>
 <c23b3ac1-68d9-bc1e-610b-955988e11055@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <c23b3ac1-68d9-bc1e-610b-955988e11055@kernel.org>
User-Agent: Mutt/1.12.0 (2019-05-25)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Aug 02, 2019 at 04:22:27PM -0600, shuah wrote:
> 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.

Ok. I will remove it and resend v4.

Regards
Suwan Kim