linux-kernel - Re: [PATCH v5 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci

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Message-ID: <20190822164011.GA7093@kroah.com>
Date:   Thu, 22 Aug 2019 09:40:11 -0700
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Suwan Kim <suwan.kim027@...il.com>
Cc:     shuah@...nel.org, valentina.manea.m@...il.com,
        stern@...land.harvard.edu, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/2] usbip: Skip DMA mapping and unmapping for urb at
 vhci

On Fri, Aug 09, 2019 at 12:54:34AM +0900, 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@...il.com>

Can you please redo this patch based on my usb-next branch that has
Christoph's DMA changes in it?  It should make your change much simpler
and smaller.

Please do that and resend the whole series.

thanks,

greg k-h