Hi,
On 5/18/2020 9:51 PM, Mathias Nyman wrote:
> On 21.4.2020 12.49, Tejas Joglekar wrote:
>> The Synopsys xHC has an internal TRB cache of size TRB_CACHE_SIZE for
>> each endpoint. The default value for TRB_CACHE_SIZE is 16 for SS and 8
>> for HS. The controller loads and updates the TRB cache from the transfer
>> ring in system memory whenever the driver issues a start transfer or
>> update transfer command.
>>
>> For chained TRBs, the Synopsys xHC requires that the total amount of
>> bytes for all TRBs loaded in the TRB cache be greater than or equal to 1
>> MPS. Or the chain ends within the TRB cache (with a last TRB).
>>
>> If this requirement is not met, the controller will not be able to send
>> or receive a packet and it will hang causing a driver timeout and error.
>>
>> This can be a problem if a class driver queues SG requests with many
>> small-buffer entries. The XHCI driver will create a chained TRB for each
>> entry which may trigger this issue.
>>
>> This patch adds logic to the XHCI driver to detect and prevent this from
>> happening.
>>
>> For every (TRB_CACHE_SIZE - 2), we check the total buffer size of
>> the SG list and if the last window of (TRB_CACHE_SIZE - 2) SG list length
>> and we don't make up at least 1 MPS, we create a temporary buffer to
>> consolidate full SG list into the buffer.
>>
>> We check at (TRB_CACHE_SIZE - 2) window because it is possible that there
>> would be a link and/or event data TRB that take up to 2 of the cache
>> entries.
>>
>> We discovered this issue with devices on other platforms but have not
>> yet come across any device that triggers this on Linux. But it could be
>> a real problem now or in the future. All it takes is N number of small
>> chained TRBs. And other instances of the Synopsys IP may have smaller
>> values for the TRB_CACHE_SIZE which would exacerbate the problem.
>>
>> Signed-off-by: Tejas Joglekar <joglekar@xxxxxxxxxxxx>
>> ---
>> Changes in v2:
>> - Removed redundant debug messages
>> - Modified logic to remove unnecessary changes in hcd.c
>> - Rename the quirk
>>
>> drivers/usb/host/xhci-ring.c | 2 +-
>> drivers/usb/host/xhci.c | 125 +++++++++++++++++++++++++++++++++++++++++++
>> drivers/usb/host/xhci.h | 4 ++
>> 3 files changed, 130 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
>> index a78787bb5133..2fad9474912a 100644
>> --- a/drivers/usb/host/xhci-ring.c
>> +++ b/drivers/usb/host/xhci-ring.c
>> @@ -3291,7 +3291,7 @@ int xhci_queue_bulk_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
>>
>> full_len = urb->transfer_buffer_length;
>> /* If we have scatter/gather list, we use it. */
>> - if (urb->num_sgs) {
>> + if (urb->num_sgs && !(urb->transfer_flags & URB_DMA_MAP_SINGLE)) {
>> num_sgs = urb->num_mapped_sgs;
>> sg = urb->sg;
>> addr = (u64) sg_dma_address(sg);
>> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
>> index fe38275363e0..15f06bc6b1ad 100644
>> --- a/drivers/usb/host/xhci.c
>> +++ b/drivers/usb/host/xhci.c
>> @@ -1256,6 +1256,106 @@ EXPORT_SYMBOL_GPL(xhci_resume);
>>
>> /*-------------------------------------------------------------------------*/
>>
>> +static int xhci_map_temp_buffer(struct usb_hcd *hcd, struct urb *urb)
>> +{
>> + void *temp;
>> + int ret = 0;
>> + unsigned int len;
>> + unsigned int buf_len;
>> + enum dma_data_direction dir;
>> + struct xhci_hcd *xhci;
>> +
>> + xhci = hcd_to_xhci(hcd);
>> + dir = usb_urb_dir_in(urb) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
>> + buf_len = urb->transfer_buffer_length;
>> +
>> + temp = kzalloc_node(buf_len, GFP_ATOMIC,
>> + dev_to_node(hcd->self.sysdev));
>> +
>> + if (usb_urb_dir_out(urb))
>> + len = sg_pcopy_to_buffer(urb->sg, urb->num_sgs,
>> + temp, buf_len, 0);
>> +
>> + urb->transfer_buffer = temp;
>> + urb->transfer_dma = dma_map_single(hcd->self.sysdev,
>> + urb->transfer_buffer,
>> + urb->transfer_buffer_length,
>> + dir);
>> +
>> + if (dma_mapping_error(hcd->self.sysdev,
>> + urb->transfer_dma)) {
>> + ret = -EAGAIN;
>> + kfree(temp);
>> + } else {
>> + urb->transfer_flags |= URB_DMA_MAP_SINGLE;
>
> Not sure if using URB_DMA_MAP_SINGLE to flag that this urb is boucebuffered is
> appropriate.
>
> If Greg or Alan don't object then it's fine for me as well.
>
>
>
@Greg/Alan do you suggest any change for the flag here?
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +static bool xhci_urb_temp_buffer_required(struct usb_hcd *hcd,
>> + struct urb *urb)
>> +{
>> + bool ret = false;
>> + unsigned int i;
>> + unsigned int len = 0;
>> + unsigned int buf_len;
>> + unsigned int trb_size;
>> + unsigned int max_pkt;
>> + struct scatterlist *sg;
>> + struct scatterlist *tail_sg;
>> +
>> + sg = urb->sg;
>> + tail_sg = urb->sg;
>> + buf_len = urb->transfer_buffer_length;
>> + max_pkt = usb_endpoint_maxp(&urb->ep->desc);
>> +
>> + if (!urb->num_sgs)
>> + return ret;
>> +
>> + if (urb->dev->speed >= USB_SPEED_SUPER)
>> + trb_size = TRB_CACHE_SIZE_SS;
>> + else
>> + trb_size = TRB_CACHE_SIZE_HS;
>> +
>> + if (urb->transfer_buffer_length != 0 &&
>> + !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
>> + for_each_sg(urb->sg, sg, urb->num_sgs, i) {
>> + len = len + sg->length;
>> + if (i > trb_size - 2) {
>> + len = len - tail_sg->length;
>> + if (len < max_pkt) {
>> + ret = true;
>> + break;
>> + }
>> +
>> + tail_sg = sg_next(tail_sg);
>> + }
>> + }
>> + }
>> + return ret;
>> +}
>> +
>> +static void xhci_unmap_temp_buf(struct urb *urb)
>> +{
>> + struct scatterlist *sg;
>> + unsigned int len;
>> + unsigned int buf_len;
>> +
>> + sg = urb->sg;
>> + buf_len = urb->transfer_buffer_length;
>> +
>> + if (usb_urb_dir_in(urb)) {
>> + len = sg_pcopy_from_buffer(urb->sg, urb->num_sgs,
>> + urb->transfer_buffer,
>> + buf_len,
>> + 0);
>> + }
>> +
>> + kfree(urb->transfer_buffer);
>> + urb->transfer_buffer = NULL;
>
> clear URB_DMA_MAP_SINGLE from urb->transfer_flags?
>
In current implmentation the dma_unmap is done with existing
function usb_hcd_unmap_urb_for_dma() and then buffer is copied
in the xhci_unmap_temp_buf(), so URB_DMA_MAP_SINGLE flag gets
cleared with usb_hcd_unmap_urb_for_dma().
I think in next patch set I will add logic for dma_unmap
in xhci_unmap_temp_buf() function.
> Everything else looks good do me.
> -Mathias
>
Thanks & Regards,
Tejas Joglekar
