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From: Greg KH <>
To: Suwan Kim <>
Subject: Re: [PATCH v5 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci
Date: Thu, 22 Aug 2019 09:40:11 -0700
Message-ID: <> (raw)
In-Reply-To: <>

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 <>

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.


greg k-h

  parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-08 15:54 [PATCH v5 0/2] usbip: Implement SG support Suwan Kim
2019-08-08 15:54 ` [PATCH v5 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci Suwan Kim
2019-08-08 16:18   ` shuah
2019-08-13 18:34     ` shuah
2019-08-22 16:40   ` Greg KH [this message]
2019-08-22 22:19     ` Suwan Kim
2019-08-08 15:54 ` [PATCH v5 2/2] usbip: Implement SG support to vhci-hcd and stub driver Suwan Kim
2019-08-08 16:21   ` shuah
2019-08-13 18:36     ` shuah
2019-08-22  1:52     ` Suwan Kim
2019-08-14 13:19 ` [PATCH v5 0/2] usbip: Implement SG support Christoph Hellwig
2019-08-15 13:23   ` Greg KH
2019-08-15 14:10     ` shuah
2019-08-15 15:25       ` Suwan Kim

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