usb: xhci-mtk: relax TT periodic bandwidth allocation

Currently uses the worst case byte budgets on FS/LS bus bandwidth,
for example, for an isochronos IN endpoint with 192 bytes budget, it
will consume the whole 5 uframes(188 * 5) while the actual FS bus
budget should be just 192 bytes. It cause that many usb audio headsets
with 3 interfaces (audio input, audio output, and HID) cannot be
configured.
To improve it, changes to use "approximate" best case budget for FS/LS
bandwidth management. For the same endpoint from the above example,
the approximate best case budget is now reduced to (188 * 2) bytes.

Signed-off-by: Chunfeng Yun <[e-mail]>
Cc: stable <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/host/xhci-mtk-sch.c

···
 
 static int check_sch_tt(struct mu3h_sch_ep_info *sch_ep, u32 offset)
 {
-	u32 extra_cs_count;
 	u32 start_ss, last_ss;
 	u32 start_cs, last_cs;
 
···
 		if (last_cs > 7)
 			return -ESCH_CS_OVERFLOW;
 
-		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 = 1;
-
-		cs_count += extra_cs_count;
 		if (cs_count > 7)
 			cs_count = 7; /* HW limit */
 
 		sch_ep->cs_count = cs_count;
-		/* one for ss, the other for idle */
-		sch_ep->num_budget_microframes = cs_count + 2;
+		/* ss, idle are ignored */
+		sch_ep->num_budget_microframes = cs_count;
 
 		/*
 		 * if interval=1, maxp >752, num_budge_micoframe is larger