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Subject: Re: [PATCH v2 0/2] usbip: Implement SG support
To:     Suwan Kim <suwan.kim027@gmail.com>, valentina.manea.m@gmail.com,
        stern@rowland.harvard.edu, gregkh@linuxfoundation.org
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        shuah <shuah@kernel.org>
References: <20190705164355.14025-1-suwan.kim027@gmail.com>
From:   shuah <shuah@kernel.org>
Message-ID: <7eaaf016-8da5-6089-fe19-bf62c3bbe187@kernel.org>
Date:   Fri, 19 Jul 2019 16:04:20 -0600
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On 7/5/19 10:43 AM, Suwan Kim wrote:
> There are bugs on vhci with usb 3.0 storage device. Originally, vhci
> doesn't supported SG, so USB storage driver on vhci breaks SG list
> into multiple URBs and it causes error that a transfer got terminated
> too early because the transfer length for one of the URBs was not
> divisible by the maxpacket size.
> 
> To support SG, vhci doesn't map and unmap URB for DMA to use native
> SG list (urb->num_sgs). In DMA mapping function of vhci, it sets
> URB_DMA_MAP_SG flag in urb->transfer_flags if URB has SG list and
> this flag will tell the stub driver to use SG list.
> 
> In this patch, vhci basically support SG and it sends each SG list
> entry to the stub driver. Then, the stub driver sees the total length
> of the buffer and allocates SG table and pages according to the total
> buffer length calling sgl_alloc(). After the stub driver receives
> completed URB, it again sends each SG list entry to vhci.
> 
> If HCD of the server doesn't support SG, the stub driver breaks a
> single SG reqeust into several URBs and submit them to the server's
> HCD. When all the split URBs are completed, the stub driver
> reassembles the URBs into a single return command and sends it to
> vhci.
> 
> Alan fixed vhci bug with the USB 3.0 storage device by modifying
> USB storage driver.
> ("usb-storage: Set virt_boundary_mask to avoid SG overflows")
> But the fundamental solution of it is to add SG support to vhci.
> 
> This patch works well with the USB 3.0 storage devices without Alan's
> patch, and we can revert Alan's patch if it causes some troubles.
> 
> Suwan Kim (2):
>    usbip: Skip DMA mapping and unmapping for urb at vhci
>    usbip: Implement SG support to vhci
> 
>   drivers/usb/usbip/stub.h         |   7 +-
>   drivers/usb/usbip/stub_main.c    |  52 +++++---
>   drivers/usb/usbip/stub_rx.c      | 207 ++++++++++++++++++++++---------
>   drivers/usb/usbip/stub_tx.c      | 108 +++++++++++-----
>   drivers/usb/usbip/usbip_common.c |  60 +++++++--
>   drivers/usb/usbip/vhci_hcd.c     |  29 ++++-
>   drivers/usb/usbip/vhci_tx.c      |  49 ++++++--
>   7 files changed, 391 insertions(+), 121 deletions(-)
> 

Hi Suwan,

I have been traveling and would like to test this series before I ask
Greg to pick it up.

Just a quick note that I will get to this early next week.

thanks,
-- Shuah