linux-kernel - [PATCH v2 04/18] usb: xhci-mtk: add only one extra CS for FS/LS INTR

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Message-ID: <5b9ff09f53d23cf9e5c5437db4ffc18b798bf60c.1615170625.git.chunfeng.yun@mediatek.com>
Date:   Mon, 8 Mar 2021 10:51:53 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ikjoon Jang <ikjn@...omium.org>
CC:     Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <linux-usb@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Eddie Hung <eddie.hung@...iatek.com>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        Alan Stern <stern@...land.harvard.edu>
Subject: [PATCH v2 04/18] usb: xhci-mtk: add only one extra CS for FS/LS INTR

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@...iatek.com>
---
v2: no changes
---
 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 450fa22b7dc7..59ba25ca018d 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