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| author | Nicolas Saenz Julienne <nsaenzjulienne@suse.de> | 2019-04-26 16:23:29 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-04-27 15:53:58 +0300 |
| commit | 33e39350ebd20fe6a77a51b8c21c3aa6b4a208cf (patch) | |
| tree | f39027fadd5dee7fd06773613f20c429ce3a90e1 /drivers/usb/host/xhci.h | |
| parent | 95e060e68bd98f28763adbc311797eebc4d31e0c (diff) | |
| download | linux-33e39350ebd20fe6a77a51b8c21c3aa6b4a208cf.tar.xz | |
usb: xhci: add Immediate Data Transfer support
Immediate data transfers (IDT) allow the HCD to copy small chunks of
data (up to 8bytes) directly into its output transfer TRBs. This avoids
the somewhat expensive DMA mappings that are performed by default on
most URBs submissions.
In the case an URB was suitable for IDT. The data is directly copied
into the "Data Buffer Pointer" region of the TRB and the IDT flag is
set. Instead of triggering memory accesses the HC will use the data
directly.
The implementation could cover all kind of output endpoints. Yet
Isochronous endpoints are bypassed as I was unable to find one that
matched IDT's constraints. As we try to bypass the default DMA mappings
on URB buffers we'd need to find a Isochronous device with an
urb->transfer_buffer_length <= 8 bytes.
The implementation takes into account that the 8 byte buffers provided
by the URB will never cross a 64KB boundary.
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb/host/xhci.h')
| -rw-r--r-- | drivers/usb/host/xhci.h | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h index 9334cdee382a..abbd4813e8a2 100644 --- a/drivers/usb/host/xhci.h +++ b/drivers/usb/host/xhci.h @@ -1303,6 +1303,8 @@ enum xhci_setup_dev { #define TRB_IOC (1<<5) /* The buffer pointer contains immediate data */ #define TRB_IDT (1<<6) +/* TDs smaller than this might use IDT */ +#define TRB_IDT_MAX_SIZE 8 /* Block Event Interrupt */ #define TRB_BEI (1<<9) @@ -2149,6 +2151,21 @@ static inline struct xhci_ring *xhci_urb_to_transfer_ring(struct xhci_hcd *xhci, urb->stream_id); } +/* + * TODO: As per spec Isochronous IDT transmissions are supported. We bypass + * them anyways as we where unable to find a device that matches the + * constraints. + */ +static inline bool xhci_urb_suitable_for_idt(struct urb *urb) +{ + if (!usb_endpoint_xfer_isoc(&urb->ep->desc) && usb_urb_dir_out(urb) && + usb_endpoint_maxp(&urb->ep->desc) >= TRB_IDT_MAX_SIZE && + urb->transfer_buffer_length <= TRB_IDT_MAX_SIZE) + return true; + + return false; +} + static inline char *xhci_slot_state_string(u32 state) { switch (state) { |