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Subject: Re: [PATCH v2 1/2] usbip: Skip DMA mapping and unmapping for urb at
 vhci
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>
 <20190705164355.14025-2-suwan.kim027@gmail.com>
From:   shuah <shuah@kernel.org>
Message-ID: <d10b23b3-601d-c2c6-df2e-77b2ed9adc66@kernel.org>
Date:   Mon, 22 Jul 2019 14:26:42 -0600
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Hi Suwan,

On 7/5/19 10:43 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.
> 
> 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).
> 
> 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.
> 
> To support SG, vhci_map_urb_for_dma() 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.
> 
> 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..14fc6d9f4e6a 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)
> +{
> +	dev_dbg(hcd->self.controller, "vhci does not map urb for dma\n");
> +
> +	if (urb->num_sgs)
> +		urb->transfer_flags |= URB_DMA_MAP_SG;
> +

Shouldn't this be part of patch 2. The debug message saying "no map"
and setting flag doesn't make sense.

> +       return 0;

This should be a tab and no spaces btw. chekpatch isn't happy.

> +}
> +
> +static void vhci_unmap_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
> +{
> +       dev_dbg(hcd->self.controller, "vhci does not unmap urb for dma\n");

This should be a tab and no spaces btw. chekpatch isn't happy.


WARNING: please, no spaces at the start of a line
#144: FILE: drivers/usb/usbip/vhci_hcd.c:1299:
+       return 0;$

WARNING: please, no spaces at the start of a line
#149: FILE: drivers/usb/usbip/vhci_hcd.c:1304:
+       dev_dbg(hcd->self.controller, "vhci does not unmap urb for dma\n");$

total: 0 errors, 2 warnings, 31 lines checked


> +}
> +
>   static const struct hc_driver vhci_hc_driver = {
>   	.description	= driver_name,
>   	.product_desc	= driver_desc,
> @@ -1304,6 +1320,9 @@ static const struct hc_driver vhci_hc_driver = {
>   
>   	.get_frame_number = vhci_get_frame_number,
>   
> +	.map_urb_for_dma = vhci_map_urb_for_dma,
> +	.unmap_urb_for_dma = vhci_unmap_urb_for_dma,
> +
>   	.hub_status_data = vhci_hub_status,
>   	.hub_control    = vhci_hub_control,
>   	.bus_suspend	= vhci_bus_suspend,
> 

thanks,
-- Shuah