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

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Message-ID: <a20e5721-d1ff-ab17-d4bb-ceae5829e647@kernel.org>
Date:   Tue, 13 Aug 2019 12:34:55 -0600
From:   shuah <shuah@...nel.org>
To:     Suwan Kim <suwan.kim027@...il.com>, valentina.manea.m@...il.com,
        gregkh@...uxfoundation.org, stern@...land.harvard.edu
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        shuah <shuah@...nel.org>
Subject: Re: [PATCH v5 1/2] usbip: Skip DMA mapping and unmapping for urb at
 vhci

On 8/8/19 10:18 AM, shuah wrote:
> On 8/8/19 9:54 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@...il.com>
>> ---
>> v4 - v5
>> - Replace pr_err() with dev_err() in the error path.
>>
>> v3 - v4
>> - Replace WARN_ON() with pr_err() in the error path.
>>
>> v2 - v3
>> - Move setting URB_DMA_MAP_SG flag to the patch 2.
>> - Prevent isoc pipe from using SG buffer.
>>
>> v1 - v2
>> - Add setting URB_DMA_MAP_SG flag in urb->transfer_flags to tell
>> stub driver to use SG buffer.
>> ---
>>   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..ea82b932a2f9 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) {
>> +        dev_err(&urb->dev->dev, "SG is not supported for isochronous 
>> transfer\n");
>> +        return -EINVAL;
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +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");
>> +}
>> +
>>   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,
>>
> 
> Looks good to me.
> 
> Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>
> 

Greg!

Please pick this one up.

Acked-by: Shuah Khan <skhan@...uxfoundation.org>

thanks,
-- Shuah