[PATCH 04/17] usb: xhci-mtk: add only one extra CS for FS/LS INTR

Chunfeng Yun
2021-03-05T09:04:05Z

In USB2 Spec:
"11.18.5 TT Response Generation
In general, there will be two (or more) complete-split
transactions scheduled for a periodic endpoint.
However, for interrupt endpoints, the maximum size of
the full-/low-speed transaction guarantees that it can
never require more than two complete-split transactions.
Two complete-split transactions are only required
when the transaction spans a microframe boundary."

Due to the maxp is 64, and less then 188 (at most in one
microframe), seems never span boundary, so use only one CS
for FS/LS interrupt transfer, this will save some bandwidth.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
---
drivers/usb/host/xhci-mtk-sch.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/host/xhci-mtk-sch.c b/drivers/usb/host/xhci-mtk-sch.c
index e3b18dfca874..817ef2815e67 100644
--- a/drivers/usb/host/xhci-mtk-sch.c
+++ b/drivers/usb/host/xhci-mtk-sch.c
@@ -408,13 +408,11 @@ static int check_sch_tt(struct usb_device *udev,
{
struct mu3h_sch_tt *tt = sch_ep->sch_tt;
u32 extra_cs_count;
- u32 fs_budget_start;
u32 start_ss, last_ss;
u32 start_cs, last_cs;
int i;

start_ss = offset % 8;
- fs_budget_start = (start_ss + 1) % 8;

if (sch_ep->ep_type == ISOC_OUT_EP) {
last_ss = start_ss + sch_ep->cs_count - 1;
@@ -450,16 +448,14 @@ static int check_sch_tt(struct usb_device *udev,
if (sch_ep->ep_type == ISOC_IN_EP)
extra_cs_count = (last_cs == 7) ? 1 : 2;
else /* ep_type : INTR IN / INTR OUT */
- extra_cs_count = (fs_budget_start == 6) ? 1 : 2;
+ extra_cs_count = 1;

cs_count += extra_cs_count;
if (cs_count > 7)
cs_count = 7; /* HW limit */

- for (i = 0; i < cs_count + 2; i++) {
- if (test_bit(offset + i, tt->ss_bit_map))
- return -ERANGE;
- }
+ if (test_bit(offset, tt->ss_bit_map))
+ return -ERANGE;

sch_ep->cs_count = cs_count;
/* one for ss, the other for idle */
--
2.18.0